Calorie Deficit Calculator
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About Calorie Deficits
Every weight-loss approach that works — low-carb, fasting, meal plans, apps — works through the same mechanism: consuming less energy than you expend. The deficit IS the diet; everything else is a strategy for making the deficit tolerable. That makes this calculator's arithmetic the honest core of the whole industry.
Enter your maintenance calories and pick a loss rate; you get the daily target, the deficit, and safety flags where the math turns aggressive. Don't know your maintenance? Compute it first — the number here is only as good as the TDEE you feed it.
Get your maintenance number from the TDEE Calculator
The Deficit Math
The convention, stated honestly:
Deficit/day = target rate (lb/week) × 500 Target = TDEE − deficit (1 lb fat ≈ 3,500 kcal — an approximation that ignores water and adaptation)
Worked example: 2,500 maintenance targeting 1 lb/week → eat ~2,000/day (a 3,500 kcal weekly deficit). The same maintenance at 2 lb/week demands 1,500 — doable for some; the calculator warns when the result crosses under ~1,200–1,500, where most people should slow down instead.
Rates and Deficits
The standard rate ladder on a 2,500-kcal maintenance:
| Rate | Daily deficit | Daily target | Monthly loss ≈ |
|---|---|---|---|
| 0.5 lb/week | 250 kcal | 2,250 | ~1 kg / 2.2 lb |
| 1 lb/week | 500 kcal | 2,000 | ~2 kg / 4.3 lb |
| 1.5 lb/week | 750 kcal | 1,750 | ~2.9 kg / 6.5 lb |
| 2 lb/week | 1,000 kcal | 1,500 | ~3.9 kg / 8.7 lb |
The gentle rates look slow until you multiply by a year — 0.5 lb/week is ~26 lb, sustained, without the rebound the steep rates invite.
Why the Scale Won't Cooperate Weekly
The 3,500-kcal rule predicts a straight line; bodies draw a squiggle. Early weeks over-deliver (glycogen and its water leave first), then progress slows below the math as metabolism adapts — a real but modest effect — and daily weight noise (sodium, carbs, hydration, hormones) can swamp a week's true fat loss in either direction. Weigh daily, trend weekly averages, and judge the plan monthly.
Protecting the loss's quality matters as much as its speed: adequate protein and resistance training bias the deficit toward fat rather than muscle, which also defends the metabolism that makes maintenance possible afterwards. And the floor warnings exist for a reason — deficits that crash intake below ~1,200 kcal trade short-term scale wins for nutrient gaps, muscle loss, and the rebound statistics that give dieting its reputation.
Frequently Asked Questions
How many calories should I eat to lose weight?
Maintenance minus 250–500: a 2,500-kcal maintenance targets 2,000–2,250 for the standard 0.5–1 lb/week. The number is personal because maintenance is — compute your TDEE first, then subtract, rather than adopting someone else's 1,500.
Is a 500-calorie deficit safe?
For most adults, yes — it's the standard recommendation's midpoint, producing ~1 lb/week. What matters is where it lands: 500 off a 1,700 maintenance dips under 1,200, where the same deficit stops being sensible without supervision. The calculator flags exactly that.
Is the 3,500-calorie rule actually true?
As physics, roughly — a pound of adipose stores ~3,500 kcal. As a prediction, only short-term: water dominates early changes and adaptation slows later loss below the line. Use it for planning; use the monthly trend, not the formula, for judging.
Why did my weight loss stall?
Usually some mix of: maintenance fell as you lost (recalculate TDEE at the new weight), portions drifted upward, and water masking fat loss. A genuine plateau at a verified deficit for 3–4 weeks means recalibrating — smaller body, smaller budget.
Should I eat back exercise calories?
If your TDEE already includes your training (activity multiplier), no — they're counted. If you used a sedentary TDEE, eating back roughly half of tracked exercise burn is the pragmatic compromise, since trackers overestimate. Pick one accounting and stay consistent.
How fast is too fast?
Past ~1% of body weight per week, muscle loss, gallstone risk, and rebound odds all climb — and under ~1,200 kcal intake, nutrient adequacy fails for most adults. The steep option exists here with warnings, not as a recommendation; sustainable and boring beats dramatic and reversed.
Methodology. This calculator uses formulas and health categories recognized by the World Health Organization (WHO) and the U.S. Centers for Disease Control and Prevention (CDC). It is reviewed and maintained by the Vast Calculators editorial team.
Last updated · July 11, 2026
Disclaimer. This tool provides estimates for general informational purposes only and is not a substitute for professional medical advice. Always consult a qualified healthcare provider before making decisions about your health.