Calorie Deficit Calculator
Estimate the daily calorie intake needed to lose a target number of pounds by a deadline, with warnings when the pace is too fast.
Important: Gradual loss of about 1 to 2 lbs per week is the pace health agencies usually describe as sustainable. Eating fewer than about 1,200 calories per day should only be done under medical supervision. The 3,500-calorie-per-pound rule is an approximation, so real progress usually slows over time. Consult a healthcare professional before starting any weight loss program.
Updated Formula covered by automated tests
A calorie deficit planner works backward from a goal: you say how many pounds you want to lose and over how many weeks, and it estimates the daily intake that would get you there. It first estimates your total daily energy expenditure (TDEE) from age, sex, height, weight and activity, then subtracts the deficit implied by your timeline.
The most useful output is often the warning rather than the number. If a deadline such as a wedding or a holiday would require losing more than 2 lb a week, or eating fewer than 1,200 calories a day, the plan is flagged in red so you can stretch the timeframe before committing to something you cannot sustain.
The formula
- TDEE
- Estimated calories burned per day at your current weight, from the Mifflin-St Jeor equation and an activity multiplier between 1.2 and 1.9
- pounds to lose
- Current weight minus goal weight, in pounds
- 3,500
- Approximate energy content of one pound of lost body weight, in kilocalories
- weeks
- The timeframe you enter; it is multiplied by 7 to spread the deficit over days
- weekly loss
- Pounds to lose divided by weeks, checked against the 2 lb per week ceiling
The 3,500-calorie figure dates back to Max Wishnofsky’s 1958 estimate of the energy stored in a pound of adipose tissue. It is a reasonable approximation for the first weeks of a diet, which is why it remains in wide use, but it treats the body as a static bank account.
In reality, as weight falls the body needs less energy, so the same intake produces a smaller deficit each week. Researchers at the US National Institutes of Health built dynamic models that account for this adaptation, and they show that losses predicted by the 3,500 rule are too optimistic over many months. Treat the plan here as a starting estimate and recalculate with your new weight every few weeks.
Worked example
Marcus is 40, 5 ft 10 in (70 in) tall and weighs 200 lb. He has a desk job, walks most evenings (lightly active, factor 1.375) and wants to reach 185 lb in 15 weeks.
- 1 Convert units: 200 lb × 0.45359237 = 90.72 kg, and 70 in × 2.54 = 177.8 cm.
- 2 BMR: 10 × 90.72 + 6.25 × 177.8 − 5 × 40 + 5 = 907.2 + 1111.25 − 200 + 5 = 1823.4 kcal.
- 3 TDEE: 1823.4 × 1.375 = 2507 kcal per day.
- 4 Total deficit: 15 lb × 3,500 = 52,500 kcal, spread over 15 × 7 = 105 days gives 500 kcal per day.
- 5 Daily target: 2507 − 500 = 2007 kcal, which is a loss of 15 ÷ 15 = 1 lb per week.
Result: Marcus would aim for about 2,000 kcal per day. At 1 lb per week and well above 1,200 kcal, the plan passes both safety checks.
Before you rely on the result
- The 3,500 kcal per pound rule ignores metabolic adaptation, so long plans usually take longer than predicted.
- TDEE is an average for people of your size and activity level; your real expenditure can differ by a few hundred calories a day.
- The 1,200 kcal floor and 2 lb per week ceiling are general guidance, not personal medical limits. A clinician can set safer targets for your situation.
Frequently asked questions
Why has my weight loss slowed even though I eat the same amount?
A lighter body burns fewer calories, so the gap between intake and expenditure shrinks as you lose weight. Water shifts can also hide fat loss for a week or two. Recalculating TDEE at your current weight usually explains most of the slowdown.
Is a 1,000 calorie daily deficit too aggressive?
For many larger adults a 1,000 kcal deficit lands at about 2 lb per week, the upper end of the pace commonly described as gradual. For smaller people the same deficit may push intake below 1,200 kcal. If the calculator flags your plan, lengthen the timeframe or speak with a doctor or registered dietitian.
Do I need to count the calories I burn exercising?
Your chosen activity level already includes typical exercise, so adding workout calories on top usually double counts them. If your routine changes a lot, pick a different activity level rather than eating back calories shown on a fitness tracker.
Who should not use a calorie deficit calculator?
Anyone who is pregnant or breastfeeding, under 18, living with diabetes or another condition that affects energy or blood sugar, or with a history of disordered eating should get individual advice from a healthcare professional instead of following a generic target.
Sources
- CDC: Steps for Losing Weight (cdc.gov)
- NIDDK Body Weight Planner (dynamic weight change model) (niddk.nih.gov)