Calorie deficit calculator
How many calories a day to reach your goal weight at a steady pace, how many weeks it takes, and the limits not to cross.
Calories a day to start
1,585 calories
11 weeks from 143 lb to 132 lb
- 499 below what you burn
- 1,508 by 132 lb
- 2,007 to stay at 132 lb
To go from 143 lb to 132 lb at 1 lb a week, you’d start at about 1,585 calories a day, 499 fewer than the 2,084 you burn now. You’d get there in about 11 weeks.
As you get lighter, you burn a little less, so keeping the pace means about 1,508 a day by the time you reach 132 lb. If you stay at 1,585 instead, it takes about 12 weeks.
I’m not a doctor or a dietitian. This is an estimate, for information only. For decisions about your health, check with a professional.
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Week by week
| Week | At 1 lb a week | Calories a day | If you stay at 1,585 |
|---|---|---|---|
| Start | 143 lb | 1,585 | 143 lb |
| 1 | 142 lb | 1,578 | 142 lb |
| 2 | 141 lb | 1,571 | 141 lb |
| 3 | 140 lb | 1,564 | 140 lb |
| 4 | 139 lb | 1,557 | 139 lb |
| 5 | 138 lb | 1,550 | 138 lb |
| 6 | 137 lb | 1,543 | 137 lb |
| 7 | 136 lb | 1,536 | 136 lb |
| 8 | 135 lb | 1,529 | 135 lb |
| 9 | 134 lb | 1,522 | 135 lb |
| 10 | 133 lb | 1,515 | 134 lb |
| 11 | 132 lb | 1,508 | 133 lb |
| 12 | — | — | 132 lb |
In short: Eat about 500 calories a day below what you burn to lose roughly 1 pound (0.45 kg) a week. US guidelines rarely go below 1,200 a day for women or 1,500 for men.
How it works
- First, the calories you burn now, as in the calorie calculator: your resting burn with the Mifflin-St Jeor equation, times your activity level.
- Then the deficit. Each kilogram lost is counted as 7,700 calories, which is 3,493 per pound: the metric form of the classic rule of 3,500 calories per pound. Divide by 7 to get a daily figure: 1 lb a week means about 499 fewer calories a day.
- Weeks to your goal = pounds to lose ÷ pounds a week. A lighter body burns less, so to keep the pace the calories go down a little every week: the table shows them week by week, next to what happens if you keep eating the starting amount.
Worked example
A moderately active 35-year-old woman, 5 ft 5 in, going from 143 lb to 132 lb at 1 lb a week. Today she burns 2,084 calories a day. 1 lb a week is 0.4536 kg × 7,700 ÷ 7 = 499 calories a day, so she starts at 1,585. 11 lb ÷ 1 lb a week = 11 weeks. At 132 lb she burns about 2,007, so the pace needs 1,508 by the end. If she stays at 1,585 every day, it takes about 12 weeks.
Sources
- CDC: Losing weight, about 1 to 2 pounds a week
- 2013 AHA/ACC/TOS obesity guideline, developed with the NHLBI: deficits, calorie ranges and very-low-calorie diets (full text, PubMed Central)
- NIDDK: Very low-calorie diet, definition
- Hall (2008), International Journal of Obesity: when the 3,500-calorie rule holds (PubMed Central)
- Hall and others (2011), The Lancet: why weight loss slows down (PubMed)
- NIDDK: Body Weight Planner
- Helms, Aragon and Fitschen (2014), Journal of the International Society of Sports Nutrition: 0.5 to 1% of body weight a week (PubMed)
- NHS 12-week weight loss plan, week 1 (UK, PDF)
Text checked on September 30, 2026
Good to know
- The 3,500-calories-a-pound rule is a simplification. An NIH researcher found it fits people with more body fat; for leaner people, more of the weight lost is lean tissue, so each pound takes fewer calories but less of it is fat.
- Your body adapts. In NIH modeling, weight responds slowly to a steady calorie intake, taking about a year to get halfway to where it settles. That’s why the plan lowers your calories week by week, and why the last column slows down.
- The warnings use the limits in the sources: 1 to 2 pounds a week (CDC), the 1,200 (women) and 1,500 (men) calories a day at the bottom of the US guidelines’ usual diet plans, and 800 calories, below which diets are done only under a doctor’s supervision.
- The plan is a straight line; real weigh-ins won’t be. For a model that also accounts for how your metabolism adapts, try the NIH’s Body Weight Planner.
- If you’re pregnant or breastfeeding, have a health condition or take medication, talk to your doctor before cutting calories.
Frequently asked questions
How big a calorie deficit is safe?
The CDC calls about 1 to 2 pounds a week a gradual, steady pace that’s easier to keep off; the NHS says 0.5 to 1 kg (1 to 2 lb) a week. US obesity guidelines usually mean 500 to 750 fewer calories a day, with women at 1,200 to 1,500 a day and men at 1,500 to 1,800. Your doctor can tell you what’s right for you.
How long will it take to lose 10 pounds?
About 10 weeks at 1 pound a week, or 5 weeks at 2 pounds a week, if you lower your calories as you go. Type your own numbers above: the table shows it week by week.
Is 1,200 calories a day enough?
1,200 is the bottom of the range US obesity guidelines use for women’s weight-loss diets; for men it’s 1,500. In the UK, the NHS plan uses 1,400 a day for most women and 1,900 for most men. Very-low-calorie diets, about 800 a day or less, are done only under medical supervision.
Why has my weight loss slowed down?
Because a lighter body burns fewer calories, the same intake makes a smaller deficit over time. NIH research found that at a steady intake, weight takes about a year to get halfway to where it settles. That’s why the calories in the plan go down a little every week.
Is a pound of fat really 3,500 calories?
It’s a rule of thumb. An NIH researcher found it roughly holds for people with more body fat, but it overstates the calories needed per pound for leaner people, because more of what they lose is lean tissue rather than fat.
Next step
- The checklistFull body, three days a week
- The short guideCalories without the obsession
- The routeGetting fit
- The guideThree workouts a week
- The calculatorMortgage payment
Related calculators
A second worked example, in metric
A lightly active man, 45, 180 cm, 100 kg, who wants to reach 90 kg at 0.5 kg a week:
- Resting burn (Mifflin-St Jeor): 10 × 100 + 6.25 × 180 − 5 × 45 + 5 = 1,905 calories.
- Daily burn: 1,905 × 1.375 (lightly active) = about 2,619.
- Deficit: 0.5 kg × 7,700 ÷ 7 = 550 calories a day, so he starts at about 2,069.
- Time: 10 kg ÷ 0.5 kg a week = 20 weeks.
- At 90 kg: resting burn 1,805, daily burn about 2,482, so the same pace needs about 1,932 a day by the end.
Both numbers stay above the 1,500 a day that US obesity guidelines use as the lower end for men, so no warning appears.
The four-week check: how to correct the estimate
The calculator starts from an equation, not from your body. After four weeks, compare the plan with your scale, using the average of your weekly weigh-ins rather than one morning:
- Plan: 4 weeks × 0.5 kg = 2 kg.
- Real result, say: 1 kg.
- What it means: 1 kg × 7,700 ÷ 28 days = about 275 calories a day of real deficit instead of 550. Either you burn about 275 less than estimated, or you eat more than you log; the NIH notes people tend to underestimate how much they eat.
- What to do: before cutting further, check portions and drinks for a week. If the log is right, lower the target by the gap, but not below the floors below.
When this calculator is the wrong tool
- Under 18: the equation was built on adults, and the NIH Body Weight Planner is also for adults 18 and over only.
- Pregnant or breastfeeding: not a time for a calorie target from a calculator. The NHS says you don’t need to “eat for 2”, but any change in intake belongs with your midwife or GP.
- A medical condition, a special diet for health reasons, or a current or past eating disorder: the NHS asks you to talk to a GP or healthcare professional before counting calories.
- Very low targets: the NIH planner warns when intake drops below 1,000 calories a day, because food group and nutrient targets aren’t met below that level; diets of about 800 or less are for medical supervision only.
Where to get structured help
- UK: the free NHS Weight Loss Plan app offers a 12-week plan; the same NHS page suggests cutting about 600 calories a day as a safe, sustainable pace. Your GP can tell you about local weight management services, some of which accept self-referral.
- US: the 2013 AHA/ACC/TOS guideline found the best results from high-intensity lifestyle programmes, with 14 or more sessions in 6 months led by a trained interventionist, followed by a maintenance programme of a year or more. If you have Medicare and a BMI of 30 or more, Part B covers behavioural counselling with your primary care provider.
- Anywhere: the guideline notes that a sustained loss of just 3% to 5% already brings clinically meaningful health benefits for people with cardiovascular risk factors, so the first goal can be small.
Sources
- 2013 AHA/ACC/TOS obesity guideline (PubMed Central)
- NIDDK (NIH): Body Weight Planner
- NHS Better Health: Calorie counting and the NHS Weight Loss Plan
- NHS: Have a healthy diet in pregnancy
- Medicare.gov: Obesity behavioral therapy
More questions
How do I know if my calorie deficit is working?
Compare the plan with the average of your weekly weigh-ins after about four weeks. Each kilogram missing from the plan over 28 days means roughly 275 calories a day less deficit than expected.
Is a 1,000-calorie deficit too much?
It means about 2 pounds a week, the top of the range the CDC calls gradual. It’s only workable if your intake stays above the guideline floors of about 1,200 a day for women and 1,500 for men; otherwise ask your doctor.
Can I use a calorie deficit while breastfeeding or pregnant?
Not from a calculator. The NIH Body Weight Planner isn’t intended for pregnant or breastfeeding women, and the NHS says changes to what you eat in pregnancy should go through your midwife or GP.
Is there a free app to follow a calorie deficit?
In the UK, the NHS Weight Loss Plan app is free and offers a 12-week plan. The NHS suggests cutting about 600 calories a day.