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Calories, by the numbers.
Calorie deficit calculator: how many calories should you eat to lose weight?
By the NexLife Medical Team · Medically reviewed by Adam Kennah, MD · Updated
Eat about 500 calories a day below your maintenance calories (TDEE) for about 1 lb a week of weight loss, by the classic math. Stay above about 1,200 (women) or 1,800 (men).
- 500 a day under your TDEE: about 1 lb a week, on paper
- Slower in real life: loss slows as your body adapts
- Under 1,200 or 1,800 a day (women, men), nutrient needs get hard to meet
What calorie deficit do you need for 1 or 2 lb a week?
- Your TDEE
- Resting burn (BMR) × 1.2 to 1.9, by activity
- 1 lb a week
- 500 calories a day under your TDEE
- 2 lb a week
- 1,000 a day under; check the floor
- The floor
- About 1,200 a day for women, 1,800 for men
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Key takeaways
- Start from your TDEE. Your BMR (Mifflin-St Jeor) times an activity factor of 1.2 to 1.9 estimates what you burn in a day.
- Subtract 500 a day for about 1 lb a week. That’s the classic 3,500-calories-a-pound math; 250 to 1,000 a day covers 0.5 to 2 lb.
- Expect slower progress. The body adapts as you lose, so the simple math overstates loss over time, a 2011 Lancet analysis showed.
- Mind the floor. Below about 1,200 calories a day (women) or 1,800 (men), nutrient needs get hard to meet, a 2025 joint advisory says.
- On a GLP-1, don’t under-eat. You may fill up fast: eat protein first, add strength training, and let your provider decide your dose.
- At NexLife, a personalized nutrition plan and a 1:1 coaching call come with every plan. Tirzepatide is $139 a month on 12 months.
Free calculator
What’s your daily calorie target to lose weight?
Enter your details, your goal weight and a pace. You’ll get a daily calorie target, the weeks to your goal and a rough date.
An estimate, not a prescription: it can’t see your health, your medicines or how your body adapts as you lose. It’s for adults. Pregnant or breastfeeding? Ask your provider instead.
The formula
How do you calculate a calorie deficit?
Work out what you burn in a day (your TDEE), then eat 250 to 1,000 calories less, depending on the pace you pick.
A calorie deficit means eating fewer calories than your body burns. The calculator above works it out in three steps:
- Your BMR (basal metabolic rate), the calories you burn at rest, from the Mifflin-St Jeor equation: for women, 10 × weight (kg) + 6.25 × height (cm) − 5 × age − 161; for men, the same but + 5 at the end.
- Your TDEE (total daily energy expenditure) = BMR × an activity factor: 1.2 sedentary, 1.375 light, 1.55 moderate, 1.725 active or 1.9 very active. These factors are conventional estimates.
- Your target = TDEE − 500 × your pace in pounds a week. The weeks to your goal = pounds to lose ÷ pace, rounded up.
| Step | The math | Result |
|---|---|---|
| Weight and height | 200 lb × 0.4536; 67 in × 2.54 | 90.72 kg; 170.18 cm |
| BMR (women) | 10 × 90.72 + 6.25 × 170.18 − 5 × 40 − 161 | 1,609.8, shown as 1,610 |
| TDEE | 1,609.8 × 1.55 (moderate) | 2,495 calories a day |
| Target | 2,495 − 500 (1 lb a week) | 1,995 calories a day |
| Time | 30 lb to lose ÷ 1 lb a week | About 30 weeks |
This is the calculator’s own starting example. Mifflin-St Jeor came from measurements of 498 healthy adults aged 19 to 78, normal-weight and with obesity. A 2005 systematic review found it the most reliable of the equations it tested, within 10% of measured resting burn for more people than any other.
Step by step
How do you start a calorie deficit, step by step?
Six steps, from your numbers to your plate. Your provider’s advice comes first.
- Find your BMR. Use the calculator above or the Mifflin-St Jeor equation. It estimates what you burn at rest from your sex, age, height and weight.
- Multiply by your activity level. Use 1.2 if you’re sedentary, up to 1.9 if you’re very active. The result is your TDEE, the calories that keep your weight steady.
- Pick a pace. Subtract 250 calories a day for about 0.5 lb a week, up to 1,000 for about 2 lb, by the classic math.
- Check the floor. Below about 1,200 calories a day for women or 1,800 for men, nutrient needs get hard to meet. If your target is lower, pick a slower pace and ask your provider.
- Build meals around protein. Eat the protein on your plate first, and add strength training to protect muscle, as a 2025 joint advisory suggests.
- Re-check as you lose. Your burn drops as your weight does, and loss slows over time. Re-run the calculator as your weight changes, and expect slower progress than the math.
The six steps above, in order. The calculator does the math in steps 1 to 4 for you; your provider’s advice comes first.
Examples
How many calories should a woman or a man eat to lose weight?
For about 1 lb a week, eat your TDEE minus 500: about 1,995 calories a day for a moderately active 40-year-old woman who is 5 ft 7 in and 200 lb, or 2,253 for a man the same size.
| Weight | Woman, sedentary | Woman, moderate | Man, sedentary | Man, moderate |
|---|---|---|---|---|
| 160 lb | 1,214 | 1,714 | 1,413 (under 1,800) | 1,971 |
| 180 lb | 1,323 | 1,855 | 1,522 (under 1,800) | 2,112 |
| 200 lb | 1,432 | 1,995 | 1,631 (under 1,800) | 2,253 |
| 220 lb | 1,541 | 2,136 | 1,740 (under 1,800) | 2,393 |
| 250 lb | 1,704 | 2,347 | 1,903 | 2,604 |
At rest, the equation gives men 166 calories a day more than women of the same weight, height and age, but the floor for men is 600 calories higher. So smaller, less active men reach it fast: the sedentary 160-lb man burns about 1,913 calories a day, only about 113 above 1,800. Ask your provider what pace is right for you.
Examples only, from the same formula as the calculator. Below about 1,200 calories a day for women or 1,800 for men, it gets hard to get enough vitamins and minerals, a 2025 joint advisory says.
Pace
How long does it take to reach a goal 20 pounds away?
About 20 weeks at 1 lb a week by the simple math: 10 weeks at 2 lb, 14 at 1.5 lb or 40 at 0.5 lb. Real loss is usually slower.
| Pace | Daily deficit | Moderate | Sedentary | Weeks for 20 lb |
|---|---|---|---|---|
| 0.5 lb a week | 250 | 2,245 | 1,682 | 40 |
| 1 lb a week | 500 | 1,995 | 1,432 | 20 |
| 1.5 lb a week | 750 | 1,745 | 1,182 (under 1,200) | 14 |
| 2 lb a week | 1,000 | 1,495 | 932 (under 1,200) | 10 |
What’s a 500-calorie deficit? Eating 500 calories a day under your TDEE: 3,500 a week, the classic estimate for a pound. That’s why the calculator subtracts 500 for each pound a week you pick. Each pace above is that math; the weeks are rounded up, as the calculator does.
Look at the sedentary column: at 1.5 or 2 lb a week, the example woman would drop under about 1,200 calories a day. A slower pace keeps her above it. The calculator warns you whenever your target falls below the floor.
The 3,500-calorie rule
Is the 3,500-calorie rule accurate?
Not over the long run. A 2011 Lancet analysis by Hall and colleagues showed the rule ignores how the body adapts to a lower weight, so it overstates loss.
Their rule of thumb, for an average adult with overweight: every 10 calories a day you cut for good moves your weight about 1 lb in the end. It takes about a year to get half of that change, and about 3 years to get 95% of it. Here’s what that means for a lasting cut of 500 calories a day:
| When | The 3,500-calorie rule | Hall’s rule of thumb |
|---|---|---|
| After about 1 year | About 52 lb | About 25 lb, half the total |
| After about 3 years | About 156 lb | About 48 lb, 95% of the total |
| In the end | No end: 1 lb a week for as long as you keep the cut | About 50 lb |
So treat the calculator’s weeks and date as optimistic. Use them to pick a pace, then expect the scale to move more slowly as you go.
Want a plan for the long run? NIH’s Body Weight Planner makes a personalized calorie and activity plan to reach a goal weight by a set time, and to keep it off afterwards. It’s for adults 18 and older, not for people who are pregnant or breastfeeding.
Safety
How big a calorie deficit is safe?
Keep your daily calories above about 1,200 if you’re a woman or 1,800 if you’re a man, unless your provider says otherwise.
Below that, it gets hard to get enough vitamins and minerals, a 2025 joint advisory from four obesity and nutrition groups says. The calculator warns you when your target falls under that line, and suggests a slower pace when there is one.
- Check your target against the floor at every pace, especially if you’re sedentary or smaller.
- Ask your provider first if you have a health condition, take medicines, or want to go below the floor.
- Pregnant or breastfeeding? Don’t use a calorie deficit calculator; ask your provider what to eat.
- Under 18? These formulas and paces are for adults.
In their words
What do NIH, the research and the label say about calorie deficits?
Four short lines: NIH’s planner, a 2005 review of the equations, Zepbound’s label and the 2025 joint advisory.
For a plan that reaches a goal weight by a set time, and keeps it off afterwards, NIH has a planner of its own.
“The Body Weight Planner allows users to make personalized calorie and physical activity plans”
National Institute of Diabetes and Digestive and Kidney Diseases (NIH), About the Body Weight Planner
The calculator starts from the Mifflin-St Jeor equation. A 2005 systematic review compared it with other equations:
“The Mifflin-St Jeor equation is more likely than the other equations tested to estimate RMR to within 10% of that measured”
Frankenfield D, Roth-Yousey L, Compher C, Comparison of predictive equations for resting metabolic rate in healthy nonobese and obese adults: a systematic review, J Am Diet Assoc 2005 (abstract)
A GLP-1 medicine works alongside a deficit, not instead of one. Zepbound’s label pairs the medicine with diet and activity:
“Administer ZEPBOUND in combination with a reduced-calorie diet and increased physical activity.”
Eli Lilly and Company, Zepbound (tirzepatide) prescribing information, revised August 2026
If you fill up fast, the order of your plate matters. The 2025 joint advisory’s tip:
“Protein-rich foods can be consumed first in a meal to increase the likelihood of sufficient consumption.”
Mozaffarian D, et al., Nutritional priorities to support GLP-1 therapy for obesity: a joint Advisory, Obesity, 2025
Stuck?
Why aren’t you losing weight in a calorie deficit?
Your real deficit may be smaller than the estimate: for the example woman, each of the first three reasons below can cut it by about 140 to 280 calories a day.
Your burn is an estimate
Mifflin-St Jeor lands within 10% of measured resting burn for more people than other equations, not for everyone. A 10% miss on her BMR moves her TDEE of 2,495 by about 250 calories a day: half the deficit.
The activity level is a guess
The factors are conventional estimates. Picking moderate (1.55) when light (1.375) fits adds about 280 calories a day to her TDEE.
Your burn drops as you lose
By the same formula, 20 lb lighter her TDEE is about 140 calories lower, so the same 1,995-calorie target is a deficit of about 360, not 500. Re-run the calculator as your weight changes.
The body adapts
Hall’s 2011 analysis found the body adapts to a lower weight, so loss slows over time, even if you keep to the same calories.
If the scale won’t move, or your target is near the floor, talk with your provider. The calculator can’t see your health or your medicines; your provider can. On tirzepatide? Our guide to a tirzepatide plateau covers what’s normal.
On a GLP-1
Do you still need a calorie deficit on a GLP-1?
Yes: Zepbound’s label pairs the medicine with a reduced-calorie diet and increased physical activity, but you may fill up fast, so watch that you don’t eat too little.
Protein first
Eat the protein on your plate first. A 2025 joint advisory suggests 80 to 120 g a day; the protein calculator works out grams per meal.
Stay above the floor
Below about 1,200 calories a day for women or 1,800 for men, it gets hard to get enough nutrients. Your provider may suggest a multivitamin.
Add strength training
The advisory says more protein alone likely won’t preserve muscle. You also need structured resistance or strength training.
Leave the dose to your provider
Never change, skip or space out a dose on your own, even if your appetite changes. Your provider decides.
Compounded tirzepatide and semaglutide aren’t FDA-approved and have no FDA label, so follow your prescriber’s instructions. Every NexLife plan includes a personalized nutrition plan and a 1:1 coaching call. More on meals: what to eat on a GLP-1.
Vial math
How many units is your tirzepatide or semaglutide dose?
On a compounded vial, the units depend on its strength. Here are the label doses at example strengths, with the math to check your own.
Tirzepatide
| Dose | mL at 25 mg/mL | Units (U-100) | On the label |
|---|---|---|---|
| 2.5 mg | 0.1 mL | 10 units | Starting dose, for 4 weeks |
| 5 mg | 0.2 mL | 20 units | A maintenance dose |
| 7.5 mg | 0.3 mL | 30 units | A step up |
| 10 mg | 0.4 mL | 40 units | A maintenance dose |
| 12.5 mg | 0.5 mL | 50 units | A step up |
| 15 mg | 0.6 mL | 60 units | The maximum, and a maintenance dose |
The math: mL = dose ÷ strength (mg per mL), and units = mL × 100. At 25 mg/mL, 10 mg is 10 ÷ 25 = 0.4 mL, or 40 units.
Semaglutide
| Weeks | Weekly dose | At 2.5 mg/mL | At 5 mg/mL |
|---|---|---|---|
| 1 to 4 | 0.25 mg | 0.1 mL (10 units) | 0.05 mL (5 units) |
| 5 to 8 | 0.5 mg | 0.2 mL (20 units) | 0.1 mL (10 units) |
| 9 to 12 | 1 mg | 0.4 mL (40 units) | 0.2 mL (20 units) |
| 13 to 16 | 1.7 mg | 0.68 mL (68 units) | 0.34 mL (34 units) |
| 17 onward | 2.4 mg | 0.96 mL (96 units) | 0.48 mL (48 units) |
The math: mL = dose ÷ strength (mg per mL); units = mL × 100. At 2.5 mg/mL, 1 mg is 1 ÷ 2.5 = 0.4 mL, or 40 units. At 5 mg/mL, the same 1 mg is 0.2 mL, or 20 units.
25 mg per mL is an example only: it’s the strength of the 15 mg multi-dose vial on Zepbound’s label (15 mg per 0.6 mL). Read the strength on your own vial’s label; your provider sets your dose, in steps at least 4 weeks apart. Every step: the tirzepatide dosage chart. Both strengths are examples only. The same dose is a different number of units at a different strength, so read the strength on your own vial’s label. Your prescription sets your dose and schedule, which may differ from these label steps. Every step: the semaglutide dosage chart.
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Calorie deficit questions
Fair questions about NexLife
- Will my price go up with my dose?
- No. You pay the same at every dose.
- What if I’m not prescribed?
- You aren’t charged for medication.
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- Yes, by email. It takes effect 30 days after we receive it. Plans renew until you cancel; our cancellation policy has the details.
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How many calories should I eat to lose weight?
Start from your maintenance calories (TDEE) and subtract 250 to 1,000 a day, for about 0.5 to 2 lb a week by the classic math. For a moderately active 40-year-old woman, 5 ft 7 in and 200 lb, 1 lb a week means about 1,995 a day. Stay above about 1,200 calories (women) or 1,800 (men).
How much weight will I lose with a 500-calorie deficit?
About 1 lb a week by the classic 3,500-calorie rule, but less over time. Hall’s 2011 rule of thumb for an average adult with overweight: a lasting 500-calorie cut leads to about 50 lb in the end, about half in the first year. Your results will differ. Keep your target above about 1,200 calories (women) or 1,800 (men).
How big a calorie deficit is safe?
Keep your calories above about 1,200 a day if you’re a woman or 1,800 if you’re a man, unless your provider says otherwise: below that, it gets hard to get enough vitamins and minerals, a 2025 joint advisory says. The calculator warns you when your target goes under that line. Ask your provider before a big cut.
How long does it take to reach a goal 20 pounds away?
About 20 weeks at 1 lb a week by the simple math, or 10 at 2 lb, 14 at 1.5 lb and 40 at 0.5 lb. Real loss usually takes longer, as it slows over time. Faster paces can take you under about 1,200 calories a day (women) or 1,800 (men); the calculator warns you if they do.
Why am I in a calorie deficit but not losing weight?
Your real deficit may be smaller than the estimate. The equation can miss your burn by 10% or more, one activity level too high adds about 280 calories in the example, and your burn drops as you lose. Before you cut more, check the floor, about 1,200 calories a day (women) or 1,800 (men), and ask your provider.
What’s the difference between BMR, TDEE and a calorie deficit?
BMR is what you burn at rest. TDEE is your BMR times an activity factor: the calories that hold your weight steady. A deficit is how far below your TDEE you eat. For the example woman: a BMR of 1,610, a TDEE of 2,495 when moderately active, and 1,995 a day for a 500-calorie deficit.
How accurate is a calorie deficit calculator?
It’s a starting estimate, not a measurement. Mifflin-St Jeor predicts resting burn within 10% of measured for more people than other equations tested, a 2005 review found, and activity factors are conventional estimates. Weight loss also slows over time, so treat the weeks and date as optimistic.
Do I need a calorie deficit on tirzepatide or semaglutide?
Yes. Zepbound’s label pairs the medicine with a reduced-calorie diet and increased physical activity. On a GLP-1 you may fill up fast, so watch that you don’t eat too little: put protein first, add strength training, and stay above about 1,200 calories (women) or 1,800 (men). Your provider decides your dose.
Does NexLife help with calories and nutrition?
Yes. Every NexLife plan includes a personalized nutrition plan and a 1:1 coaching call. Compounded tirzepatide is $139 a month on the 12-month plan or $169 month to month; compounded semaglutide is $119 on the 12-month plan or $139 month to month. Questions come to NexLife 24/7.
Is a 1,000-calorie deficit safe?
Only if it keeps you above the floor. A 1,000-calorie daily deficit is about 2 lb a week by the classic math, but it can take you under about 1,200 calories a day (women) or 1,800 (men). The sedentary example woman would drop under 1,200 at that pace. Ask your provider first.
How many calories are in a pound of weight?
About 3,500, by the classic estimate. That’s why a 500-calorie daily deficit, 3,500 a week, counts as about 1 lb a week. A 2011 Lancet analysis showed the rule ignores how the body adapts to a lower weight, so it overstates loss over time.
Which activity level should you pick on the calculator?
Match your usual week. Sedentary (1.2) means little or no exercise; light (1.375), 1 to 3 days a week; moderate (1.55), 3 to 5; active (1.725), 6 or 7; very active (1.9), hard daily exercise or a physical job. Picking a level too high can add about 280 calories a day to your TDEE.
Important safety information
Compounded tirzepatide and semaglutide are not FDA-approved, and the FDA hasn’t reviewed them for safety, effectiveness or quality. A provider prescribes them only when they offer a significant difference for you compared with an FDA-approved product. Both medicines may cause thyroid tumors, including cancer: don’t use either if you or a family member has had medullary thyroid carcinoma (MTC) or multiple endocrine neoplasia syndrome type 2 (MEN 2).
Read the full safety information
In studies with rodents, both medicines caused thyroid tumors; it isn’t known whether they cause them in people. Tell your provider if you notice a lump or swelling in your neck, hoarseness, trouble swallowing or shortness of breath. Serious side effects can include inflammation of the pancreas (pancreatitis), gallbladder problems, low blood sugar (especially with insulin or sulfonylureas), kidney problems from dehydration, severe stomach problems, serious allergic reactions, vision changes in people with type 2 diabetes, and a faster heart rate. Tell your care team before any surgery or procedure that uses anesthesia or deep sedation. Don’t combine either medicine with other
Tirzepatide can make birth control pills less effective: switch to a non-oral method, or add a barrier method such as condoms, for 4 weeks after you start and for 4 weeks after each dose increase. Both medicines may harm an unborn baby. Semaglutide should be stopped at least 2 months before a planned pregnancy. Tell your provider right away if you’re pregnant, planning to be, or breastfeeding.
This is a summary, not the complete safety information. Read the full Prescribing Information for FDA-approved tirzepatide (Zepbound) and semaglutide (Wegovy), and talk with your provider. You can report side effects to the FDA at
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Who wrote and medically reviewed this page?
Leads the NexLife Medical Team, which writes and medically reviews NexLife’s guides, including this one.
Checked the formulas against Mifflin 1990 and Frankenfield 2005, the weight-change math against Hall 2011 (The Lancet), and the calorie floor against the 2025 joint advisory (Obesity, August 2025).
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Sources
- Mifflin MD, St Jeor ST, Hill LA, Scott BJ, Daugherty SA, Koh YO. A new predictive equation for resting energy expenditure in healthy individuals. Am J Clin Nutr. 1990;51(2):241-247.
- Frankenfield D, Roth-Yousey L, Compher C. Comparison of predictive equations for resting metabolic rate in healthy nonobese and obese adults: a systematic review. J Am Diet Assoc. 2005;105(5):775-789.
- National Cancer Institute, ADOPT. REE-Mifflin St.Jeor equation, Total EE, Physical Activity Level (PAL).
- Hall KD, Sacks G, Chandramohan D, Chow CC, Wang YC, Gortmaker SL, Swinburn BA. Quantification of the effect of energy imbalance on bodyweight. Lancet. 2011;378(9793):826-837.
- National Institute of Diabetes and Digestive and Kidney Diseases (NIH). Body Weight Planner.
- Mozaffarian D, Agarwal M, Aggarwal M, et al. Nutritional priorities to support GLP-1 therapy for obesity: a joint advisory from the American College of Lifestyle Medicine, the American Society for Nutrition, the Obesity Medicine Association and The Obesity Society. Obesity (Silver Spring). 2025;33(8):1475-1503.
- Eli Lilly and Company. Zepbound (tirzepatide) prescribing information. Revised August 2026.
- Eli Lilly and Company, via Drugs@FDA. ZEPBOUND (tirzepatide) injection, for subcutaneous use: prescribing information, revised 02/2026.
- Novo Nordisk. Wegovy (semaglutide) prescribing information.
- Novo Nordisk. Wegovy dosing schedule.
- U.S. Food and Drug Administration. Compounding and the FDA: Questions and Answers.
- U.S. Food and Drug Administration. FDA alerts health care providers, compounders and patients of dosing errors associated with compounded injectable semaglutide products.
- U.S. Food and Drug Administration. FDA’s concerns with unapproved GLP-1 drugs used for weight loss.
- U.S. Food and Drug Administration. MedWatch: The FDA Safety Information and Adverse Event Reporting Program.
- NexLife. Compounded tirzepatide plans.
- NexLife. Compounded semaglutide plans.
- LegitScript. LegitScript certification record for NexLife.us.
- Ro: weight loss program pricing. Checked November 1, 2026.
- Hims: Zepbound KwikPen. Checked November 1, 2026.
- Hims: Wegovy pill and pen, with membership. Checked November 1, 2026.
- Mochi Health: FAQs (membership and medication prices). Checked November 1, 2026.
- Embody: compounded tirzepatide, one-month supply. Checked November 1, 2026.
- Embody: compounded semaglutide, one-month supply. Checked November 1, 2026.