Calorie Deficit Calculator

How the calculator works

Losing weight comes down to one principle: take in fewer calories than you burn. The hard part is knowing what "fewer" means for you. This tool works it out in two steps.

First it estimates your maintenance calories — the amount that keeps your weight stable — using the Mifflin-St Jeor equation, widely regarded as one of the most accurate formulas for resting metabolic rate. It calculates your BMR (the energy your body uses at complete rest) from your age, sex, height, and weight, then multiplies it by an activity factor to reflect how much you move.

Then it subtracts a deficit based on your chosen pace. A kilogram of body fat stores roughly 7,700 calories, so trimming about 550 calories a day adds up to around half a kilo of loss per week. Pick "Steady" and you're targeting a comfortable, sustainable rate; pick "Aggressive" and the deficit — and the difficulty of sticking to it — goes up.

Choosing a sensible pace

Faster isn't better. A large, sudden deficit is harder to sustain, tends to cost you muscle alongside fat, and often triggers the rebound that undoes the whole effort. For most people a loss of 0.25 to 0.75 kg (0.5 to 1.5 lb) per week is the sweet spot — fast enough to stay motivated, slow enough to keep. If your target drops below roughly 1,200 calories a day (women) or 1,500 (men), ease off the pace rather than pushing through.

The number is a starting point, not a verdict

Every calculator gives an estimate. Real energy needs vary with body composition, genetics, sleep, stress, and daily movement you don't think of as exercise. The right move is to treat this target as a hypothesis: eat to it consistently for two to three weeks, watch your weight trend (not day-to-day noise), and nudge the number up or down based on what actually happens. Consistency in how you track matters far more than precision in any single day.

That last part is where most people come unstuck — not the maths, but sustaining the awareness. Rekkon is built for exactly that: you just say what you ate and it keeps the running tally, so hitting a target like this one stays effortless instead of turning into a chore.

This calculator provides general estimates for educational purposes and isn't medical or dietary advice. If you're pregnant, have a medical condition, or a history of disordered eating, talk to a doctor or registered dietitian before starting a calorie deficit.