Calorie deficit calculator: maintenance, target and realistic timeframe

A calorie deficit is simple arithmetic and difficult practice. The arithmetic part is worth getting right anyway, because it sets expectations: most people either aim far too aggressively and stop, or underestimate maintenance and wonder why nothing changes.

Where these numbers come from

Maintenance is estimated with the Mifflin-St Jeor equation multiplied by an activity factor. The deficit uses the conventional figure of roughly 7,700 kcal per kilogram of body fat. Both are population averages: individuals vary, and the activity multiplier in particular is a rough bracket rather than a measurement.

How to read the result

Treat it as a starting point to test, not a number to obey. Eat at the target for two to three weeks and track the trend rather than daily weight, which moves with water and food volume. If the trend does not match the prediction, your real maintenance differs from the estimate — adjust the intake, not your confidence in the scale.

Common mistakes

• Choosing too aggressive a rate. Faster loss is harder to sustain and costs more muscle.
• Overstating activity level. Most people sit in a lower bracket than they select.
• Reading daily weight as progress. Weekly averages are the only useful signal.
• Forgetting that maintenance falls as weight does, so the same intake becomes a smaller deficit over time.

If you have a history of disordered eating, a medical condition, or are pregnant or breastfeeding, this tool is not appropriate — speak to a professional instead.