Calorie Deficit Calculator
Enter your maintenance calories and how fast you want to lose. The calculator works backwards to a daily intake, and flags rates that will cost you muscle.
Your results
Based on roughly 7,700 kcal per kilogram of body fat. Real rates vary, and your maintenance level falls as you lose weight — recalculate every 5 kg.
Why 0.5–1.0% per week
Reviews of fat-loss phases in resistance-trained people converge on losing 0.5 to 1.0% of body weight per week as the range that best preserves fat-free mass. For an 80 kg person that is 400–800 g a week.
Faster is possible and costs more muscle, because a larger share of the shortfall comes from lean tissue and because training quality degrades — which removes the signal telling your body to keep the muscle it has.
What the calculator cannot know
The 7,700 kcal-per-kilogram figure is a reasonable average and not a constant. Early weight loss includes water and glycogen, so week one usually overshoots the prediction and week two appears to stall.
Your maintenance also falls as you get smaller — roughly 20–25 kcal per kg lost, before any adaptive effect. Recalculate after every 5 kg or so rather than running the same number for six months.
Common questions
What if the intake looks very low?
Reduce the rate rather than accepting it. Below about 1,500 kcal for men or 1,200 for women, dieting becomes hard to sustain and nutritionally tight.
Should I eat back exercise calories?
No — if you chose an activity level that already includes your training, it is counted. Adding it twice is the most common tracking error.
Why am I not losing at the predicted rate?
Usually intake is higher than recorded, or daily movement has dropped. Give it three weeks of weekly averages before adjusting.
Is a bigger deficit ever appropriate?
With a lot of fat to lose, the higher end of the percentage range is already a large absolute deficit. Beyond that, muscle loss and adherence both suffer.
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Track the numbers, not just calculate them
MyFitsy stores your weight, measurements and every session, so the figures above become a trend instead of a one-off.
