Calorie Deficit Calculator

Your daily deficit is your target weekly rate × the energy stored per unit of body mass ÷ 7 — so 0.5 kg/week × 7,700 ÷ 7 = 550 kcal/day — subtracted from your maintenance calories. A safe deficit is roughly 550–1,100 kcal per day on the kilogram basis, or 500–1,000 on the pound basis, the range that produces the 0.5–1 kg (1–2 lb) weekly loss CDC, WHO and AHA guidance points to.

How a calorie deficit works

A deficit simply means eating fewer calories than you burn; your body covers the gap from stored energy, mostly body fat, and you lose weight. Because a kilogram of body mass stores roughly 7,700 calories (about 3,500 per pound), your chosen weekly rate translates into a specific daily deficit. The tool subtracts that deficit from your maintenance calories to give a target intake.

You need your maintenance figure first — the TDEE calculator estimates it, and the BMR calculator shows the resting floor you shouldn't drop below for long. For a projected finish date, feed the same numbers into the weight-loss timeline calculator; for the mechanism itself, start with what a calorie deficit is.

Choosing a safe deficit

Steady beats fast. Health authorities point to 0.5–1 kg (1–2 lb) per week — a 550–1,100 kcal daily deficit on the kilogram basis, 500–1,000 on the pound basis — as the sustainable range that best preserves muscle. Bigger deficits work faster but are harder to hold and cost more lean tissue. The calculator flags rates above that, and target intakes that fall below sensible minimums. Once you have your intake, split it with the macro calculator or set protein alone with the protein intake calculator.

Weekly rate and the deficit it needs

Deficit = weekly rate × energy per unit ÷ 7 (7,700 kcal/kg; 3,500 kcal/lb). The kg and lb rows differ slightly because 1 kg = 2.2 lb.

The same meal plan, ten kilograms later

This calculator asks for your maintenance calories once and then treats that figure as a constant for the rest of the diet. It is not one. Maintenance is a function of your body weight, so the moment the scale starts moving, the number you typed in goes out of date — and the deficit you are actually running shrinks along with you.

Take a man of 35, 180 cm and 80 kg who trains three to five days a week. Our BMR calculator puts his resting rate at 1,755 kcal/day, and the moderate activity multiplier the TDEE calculator ships (×1.55) makes maintenance 2,720 kcal/day. Ask this tool for 0.5 kg a week and it returns a 550 kcal/day deficit and a target intake of 2,170 kcal/day. Ten kilograms later, at 70 kg, his BMR is 1,655 and maintenance is 2,565. He is still eating 2,170, so his deficit is now 395 kcal/day — 28% smaller than the one he was prescribed, on a diet he has not changed by a single calorie.

Mifflin-St Jeor exactly as our BMR calculator ships it (10 × kg + 6.25 × cm − 5 × age + 5 for men), for a 35-year-old man of 180 cm, times the moderate ×1.55 multiplier, with intake held at the 2,170 kcal/day this calculator returns on day one. Each kilogram lost takes 10 kcal/day off BMR and 15.5 off maintenance, so every 2 kg row drops 31 kcal.

This is not an error bar and it is not the calculator being wrong. The 550 was correct on the day it was typed; what changed is the body it was calculated for. The underlying quantity moved. You can see why in the Mifflin-St Jeor equation itself — weight enters it with a coefficient of 10, so ten kilograms is a hundred kilocalories of BMR, every time.

Nor, in this equation, does it depend on your sex. The weight term is 10 kcal per kilogram for men and women alike; sex only shifts the constant at the end (+5 for men, −161 for women). A woman of 35 at 80 kg and 165 cm has a lower maintenance figure — 2,317 kcal/day at the same ×1.55 — but losing the same 10 kg costs her the same 155 kcal/day, and on the same 0.5 kg a week her deficit erodes from 550 to 395 exactly as his does. What does change its size is how active you are, because the multiplier scales it: the same 10 kg costs 120 kcal/day at ×1.2 and 190 kcal/day at ×1.9, the lowest and highest activity settings these calculators ship.

What that does to the finish date

The weight-loss timeline calculator divides the weight you want to lose by your weekly rate: 10 kg at 0.5 kg a week is 20 weeks. That is the flat answer, and it assumes the deficit never moves. Hold intake at 2,170 and recompute maintenance from the current weight once a week instead, and the same 10 kg takes 23.3 weeks — 3.3 weeks longer for identical discipline.

Which plans suffer most is the part worth knowing before you choose one. The erosion depends on how much weight you lose, not how fast: 10 kg costs 155 kcal/day whether it takes ten weeks or fifty. So it is the gentle plans, the ones with the smallest deficits, where that fixed 155 kcal takes the biggest proportional bite.

Same man, same 10 kg, four rates. The 80 kg deficit is what this calculator returns; intake is then held fixed while maintenance is recomputed from that week's weight using Mifflin-St Jeor × 1.55, one recalculation per week. Flat weeks are the timeline calculator's straight-line division of 10 kg by the weekly rate.

At 0.25 kg a week the plan gives up 56% of its deficit before reaching the goal and a projected 40 weeks becomes 58; at 1 kg a week the identical 155 kcal costs 0.7 of a week. Straight-line arithmetic flatters the slow, sustainable option most — which is an argument for adjusting as you go, not for rushing.

What to do about it is straightforward: re-enter your maintenance figure as the weight comes off rather than once at the start. How often depends on the size of your deficit. To keep a 550 kcal/day deficit within 10% of target you need to recalculate about every 3.5 kg (roughly 8 lb); to hold a 275 kcal/day deficit to the same 10%, about every 1.8 kg. Put your current weight through the TDEE calculator, type the new figure into the box above, and track the real trend with the weight-loss percentage calculator.

One thing this arithmetic is not: a full account of what dieting does to your metabolism. It models a single effect — a smaller body costs less to run — so it is a floor on how far the deficit erodes, not a ceiling. Dieting also produces adaptive thermogenesis, a fall in expenditure beyond what the smaller size alone predicts; no number for it appears on this page, because none of the guidance this page cites quantifies it. Our guide to how long it takes to lose weight works the same problem from the timeline end. Either way the conclusion holds: the scale is the instrument that corrects the estimate.

Formulas: the 7,700 kcal/kg (3,500 kcal/lb) energy-equivalent rule for the deficit; Mifflin-St Jeor with the activity multipliers our BMR and TDEE calculators ship for the maintenance figures. Rates follow CDC/WHO/AHA guidance; intake minimums from the 2013 AHA/ACC/TOS guideline. The linear model overstates long-term loss, and the erosion shown here accounts only for a smaller body, not for adaptive thermogenesis — estimates, not medical advice.