How Many Calories Should You Eat to Lose Fat?

Forget generic calculators. Here's how to find the number that actually works for your body — and why it should change over time.

Every fat-loss plan starts with one number: how many calories you eat per day. Get it roughly right and the fat comes off. Get it wrong and you either stall or burn out. The good news is you don't need to guess.

Start with maintenance

Maintenance is the calories that keep your weight stable. A formula (the Mifflin-St Jeor equation) estimates it from your sex, age, height, weight and activity. That's where PRIME starts you — but a formula is only an estimate. Two people with identical stats can differ by 300+ calories.

Then create a modest deficit

To lose fat, eat below maintenance. A deficit of 15-20% (roughly 300-600 kcal) loses fat steadily while protecting muscle and energy. Crash diets of 1,000+ kcal deficits backfire: you lose muscle, your training tanks, and you rebound.

• •Aim to lose about 0.5-1% of body weight per week
• •Keep protein high to hold onto muscle
• •Don't drop below ~1,500 kcal (men) / ~1,200 kcal (women) without supervision

The part most apps miss

Your real maintenance changes as you lose weight and as your body adapts. The smartest approach is to measure it from your own data: compare your actual average intake against your weight-trend over 2-3 weeks, and adjust. That's exactly what PRIME's adaptive engine does once you've logged enough days — so your target stays honest instead of frozen at a day-one guess.