Calorie Deficit Calculator
Your maintenance calories minus a pace you can actually sustain — that's the whole game. Pick honestly, and the calculator flags targets that dip below safe territory.
Estimates, not prescriptions · the 3,500-kcal rule is a useful approximation that weakens over time · nothing you enter leaves this browser.
Spotted a mistake or have an idea? — errors get fixed and credited publicly.
Last reviewed: July 20, 2026 · Formulas verified by automated tests before every release.
How many calories should I eat to lose weight?
Maintenance (TDEE) minus your deficit: at a 2,000-kcal maintenance, a standard −500 gives a 1,500 kcal/day target and roughly 1 lb (0.45 kg) per week. The calculator above computes your TDEE from the clinical Mifflin-St Jeor equation, applies the pace you choose — and warns if the target lands under 1,200/1,500 kcal, where unsupervised dieting shouldn't go.
The deficit is the diet
Every eating plan that works — keto, fasting, meal prep, points — works through the same door: calories in below calories out, held long enough. The label on the door matters only for whether you can keep walking through it. So the honest sequence is: get maintenance right (the activity dropdown is where most plans quietly die — flattery adds 300 phantom calories), pick the gentlest pace that still moves, and let the arithmetic be boring.
Where the numbers bend
Two honest caveats the fitness internet skips. First, the 3,500-kcal pound is an approximation that decays: as weight drops, maintenance drops with it, so a fixed intake delivers a shrinking deficit — recalculate monthly. Second, the first fortnight lies in both directions: water losses exaggerate early progress, then water retention hides real fat loss. Judge trends over weeks, not days. For the fuller picture of what you burn, start at the TDEE calculator; to split the target into protein, carbs and fat, the macro calculator takes it from here; and BMI remains the rough screen, not the verdict.
Sources, assumptions and limitations
- Assumptions: TDEE via Mifflin-St Jeor × activity multiplier — estimates vary ±10% between individuals.Pace uses the 3,500 kcal ≈ 1 lb approximation; real loss slows as maintenance falls.Safety floor flags targets under 1,200 kcal (women) / 1,500 kcal (men) — below that, involve a clinician.Educational estimates, not medical advice; pregnancy, medications and conditions change the math.Nothing you enter is stored or transmitted.
- Sources: ·
- Last reviewed: by the CalcNotebook team
Frequently asked questions
How big should my calorie deficit be?
A 500 kcal/day deficit — roughly 1 lb (0.45 kg) per week — is the standard sustainable starting point. Gentler (250) fits people close to goal weight; larger deficits (750–1000) lose more muscle, feel worse, and are harder to keep. If the target falls below 1,200 kcal (women) or 1,500 kcal (men), the calculator flags it — that territory belongs with a clinician.
Is the 3,500-calories-per-pound rule accurate?
It's a useful approximation for the first weeks, not a law of physics. As you lose weight your TDEE drops (a lighter body burns less), so the same intake produces a shrinking deficit. Recalculate every 10 lb or monthly, and expect the scale to slow — that's arithmetic, not failure.
Should I cut calories or exercise more?
Both move the same number: a deficit is calories out minus calories in. Food is usually the bigger lever (skipping a 500-kcal pastry takes seconds; burning 500 kcal runs about 5 miles), but activity protects muscle and raises the TDEE side. The honest combo: modest food cut + honest activity level, not flattery in the dropdown.
Why am I not losing weight in a deficit?
The usual suspects, in order: the deficit exists on paper but portions drifted; the activity level chosen was one notch too generous; water weight is masking fat loss (very normal for 2–4 weeks); or maintenance was overestimated. Re-measure honestly for two weeks before concluding anything — and if it still won't move, see a clinician.
Do you store my numbers?
No. Age, weight, height and targets exist only in this browser tab — nothing is uploaded or saved anywhere.