Calorie Deficit Calculator

A calorie deficit is eating less energy than you spend. Everything else — which foods, which pattern, which hours — is a means of arriving at that, not a substitute for it.

The conventional conversion is 3,500 kcal to a pound of body fat, so a 500 kcal daily shortfall is roughly a pound a week and 1,000 is roughly two. The guidelines that recommend that range recommend it because it is a rate people actually hold, not because it is the fastest arithmetic available.

250 kcal/day

≈ 0.5 lb a weekSlow, and easy to miss inside normal day-to-day variation

500 kcal/day

≈ 1 lb a weekThe usual starting point in the guidelines

750 kcal/day

≈ 1.5 lb a weekWorkable for a while, harder to eat well inside

1,000 kcal/day

≈ 2 lb a weekThe top of the recommended range, and the floor bites first here

This calculator will not print a target below 1,200 kcal a day for women or 1,500 for men. Those are the lower bounds in the US clinical guidelines for self-directed weight loss, and below them two things happen: hitting your protein and micronutrient needs stops being realistic, and adherence collapses long before the deficit has time to work.

If the deficit you chose would cross the floor, the figure shown is the floor and the reading says so. The remaining gap is closed by moving more or by accepting a slower rate — not by eating less than the floor.

Intakes below those figures are used in medicine, under supervision, with monitoring and supplementation. That is a clinical programme, not a setting on a calculator.

A deficit calculated today is correct for today. It stops being correct as you lose weight, because maintenance falls with body size — the target that produced a pound a week at the start can be close to maintenance 20 lb later.

• Maintenance is an estimate to begin with, typically within about 10% of measured expenditure.
• Unplanned movement falls when you eat less — you sit more, fidget less, take fewer steps — so the real deficit is usually smaller than the arithmetic one.
• Logged intake is routinely under-reported, by a wide margin and not deliberately.
• Weight on the scale moves with water, sodium, carbohydrate, training and the menstrual cycle, all of which are larger day to day than a 500 kcal deficit.

The practical version: pick a deficit you can hold, recalculate every 5 to 10 lb, and judge it on three weeks of weights rather than three days.

Maintenance first — the Mifflin–St Jeor resting rate multiplied by your activity factor — then the deficit is subtracted and the result is held at the floor:

Resting rate, men

(10 × kg) + (6.25 × cm) − (5 × age) + 5

Resting rate, women

(10 × kg) + (6.25 × cm) − (5 × age) − 161

Maintenance

resting rate × activity factor (1.2 – 1.9)

Target

the greater of (maintenance − deficit) and the floor

Floor

1,200 kcal/day women · 1,500 kcal/day men

The rate printed under the figure is the deficit actually applied — after the floor — divided by 3,500 and multiplied by seven, which is why it falls short of the slider when the floor is doing the work.