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Uses ~7,700 kcal per kg of body fat. A 500 kcal/day deficit gives the NHS-recommended 0.5-1kg (1-2lb) a week; steeper deficits are harder to sustain and lose more muscle. Real progress arrives in steps, not lines: weekly averages beat daily weigh-ins. Set the deficit from your TDEE, and don't eat below ~1,400 kcal (women) / 1,900 (men) without medical advice.
What The Calorie Deficit Calculator Works Out
- Weekly loss rate: the daily deficit x 7 divided by roughly 7,700 kcal per kg of body fat (the 3,500-calories-per-pound rule). A 500 kcal daily deficit predicts about 0.45 kg or a pound a week, the rate the NHS and most guidance bless as sustainable.
- Time to goal: total kilos to lose x 7,700, divided by the daily deficit. Seven kilos at 500 kcal a day is a fifteen-week project rather than a fortnight's crash.
- Total to lose: current minus goal weight in kg and pounds.
- Weights entered in (advanced): type both weights in stones (as decimals) or pounds instead of kg.
- Custom daily deficit (advanced): any figure in place of the three presets. Steeper deficits trade speed for muscle loss, hunger and rebound risk, the trio behind the finding that most rapid losses regain.
- Maintenance calories and daily intake (advanced): building the deficit starts from TDEE, not from a magic intake number. Enter your maintenance figure to see what to eat each day, checked against the floors of about 1,400 kcal for women and 1,900 for men below which you need medical supervision rather than ambition.
- Deficit from exercise (advanced): the share of the deficit you plan to create by moving more rather than eating less, which raises the daily intake. Exercise's calories are routinely overestimated and its appetite effects vary, but its muscle-preserving role in a deficit, alongside protein's, is the best-evidenced part of the whole field.
- Metabolic slowdown (advanced): the arithmetic is static while the body is not. Metabolism adapts modestly downward as weight falls and a smaller body needs fewer calories, so the deficit that once cut 500 shrinks. Entering 5% to 10% lengthens the timeline realistically; water weight also flatters the first fortnight and plateaus slander it, so the trend through weekly averages is the only honest instrument.
- Monthly rate, goal date and milestones (advanced): loss per month, the weekly loss as a percentage of bodyweight (0.5% to 1% is the usual sustainable band), a calendar date for the goal, and a week-by-week milestone table in kg and stones. Maintenance is the actual finish line the timeline should be planned toward.
- Caveats: the deficit someone can hold cheerfully for four months beats the perfect one abandoned in three weeks. This arithmetic is for adults and not for pregnancy, adolescence or anyone with a history of disordered eating, for whom calorie counting is often the wrong tool. If eating or weight is causing you distress, your GP is the right first conversation, and support exists.
Further reading: NHS: healthy weight.