Calorie Deficit Calculator
A calorie deficit means eating fewer calories than you burn, and it is what drives weight loss. This calculator takes the number of calories you cut below your maintenance level (TDEE) each day and estimates the resulting weekly weight loss using the traditional rule that one pound of body weight is roughly 3,500 calories. Important caveat: that 3,500-kcal-per-pound rule is a simplified approximation. It works as a rough early-stage guide but overstates loss over the long run because it ignores metabolic adaptation — your body burns less as you get lighter (Hall et al. 2013). Treat the estimate as a planning figure, not a promise.
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Default result: 1.00
Calorie Deficit Calculator · Result
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Estimated weight loss per week
500
- Weekly calorie deficit
- 3,500
This calculator provides general estimates for educational purposes only and is not medical advice. Results are based on population formulas and may not reflect your individual circumstances. Consult a qualified healthcare professional before making changes to your diet, exercise, or health routine.
Reviewed by the calculators.dev team · Last updated 2026-06-23
Formula reviewed against Wishnofsky M. Caloric equivalents of gained or lost weight. 1958 (the 3,500-kcal/lb rule)
How to calculate
Enter the daily calorie deficit — the calories you eat below your maintenance level. The calculator multiplies it by 7 for a weekly deficit, then divides by 3,500 to estimate pounds lost per week. A 500 kcal/day deficit is 3,500 kcal/week, which the rule equates to about 1 lb/week. Find your maintenance level with the TDEE calculator first. A deficit of 300–500 kcal/day is a common, sustainable starting point; very aggressive deficits are hard to maintain and can cost lean mass.
weekly_deficit = daily_deficit × 7, then estimated_loss_lb = weekly_deficit ÷ 3,500. Variables: daily_deficit is the calories below maintenance per day and 3,500 is the Wishnofsky kcal-per-pound constant. This constant is a simplified linear approximation: real loss is non-linear and slows over time as metabolism adapts, so the formula overstates long-term loss (Hall et al. 2013, PMC3859816). Use it for a rough early estimate only.
Example calculation
A 500 kcal/day deficit adds up to 500 × 7 = 3,500 kcal over a week. Dividing by the 3,500-kcal-per-pound rule gives an estimated 1.0 lb of weight loss per week. In practice loss slows over time as the body adapts (Hall et al. 2013), so treat 1 lb/week as an early-stage estimate, not a guarantee.
- lbsPerWeek
- 1.00 lb/week
- weeklyDeficitKcal
- 3,500 kcal
Assumptions
- The 3,500-kcal-per-pound rule is a simplified approximation (Wishnofsky 1958); it overstates long-term loss because it ignores metabolic adaptation (Hall et al. 2013).
- The estimate assumes the deficit is held steady and that maintenance calories stay constant — in reality both change as you lose weight.
- Weekly weight can swing with water, sodium, and glycogen, so scale-weight rarely tracks the calorie estimate exactly week to week.
Common mistakes
- Trusting the 3,500-kcal rule for months. It is roughly right early on but increasingly overstates loss as you get lighter and your metabolism adapts.
- Setting too large a deficit. Very aggressive cuts are hard to sustain, increase muscle loss, and often backfire — a moderate 300–500 kcal/day deficit is usually better.
- Forgetting to base the deficit on an up-to-date maintenance level. As you lose weight, your TDEE falls, so the same intake becomes a smaller deficit.
Frequently asked questions
How many calories is one pound of weight loss?
The traditional rule is about 3,500 calories per pound. This is a simplified estimate — it is reasonable in the short term but overstates long-term loss because your metabolism adapts as you get lighter.
Is the 3,500-calorie rule accurate?
Only roughly, and mainly early on. Research (Hall et al. 2013) shows real weight loss is non-linear and slows over time, so the rule predicts more loss than people actually see over months. Use it as a starting estimate, not a guarantee.
What is a safe calorie deficit?
A deficit of about 300–500 kcal/day (roughly 0.5–1 lb/week) is a common, sustainable target for many adults. Larger deficits are harder to maintain and can cost muscle. Talk to a healthcare professional before a steep cut.
Why did my weight loss slow down?
As you lose weight your body needs fewer calories, so a fixed deficit shrinks over time — this is metabolic adaptation. Recalculate your maintenance calories periodically and adjust your intake.