Calorie Deficit Calculator: Daily Calories and Goal Date

Short answer

Choose how fast you want to lose weight as a percentage of your body weight per week. The calculator turns that into a daily deficit with the 7,700 kcal per kg rule and subtracts it from your TDEE.

Example with made-up numbers: TDEE 2,600 kcal, current weight 80 kg, goal 72 kg, pace 0.5% a week. That is 0.4 kg a week, a deficit of 440 kcal a day, so about 2,160 kcal a day. At a steady 0.4 kg a week, the 8 kg would take 20 weeks. In practice it usually takes longer (see below).

The math

• Weekly loss (kg) = current weight × pace
• Daily deficit (kcal) = weekly loss × 7,700 ÷ 7
• Daily calories = TDEE − daily deficit
• Weeks to goal = (current weight − goal weight) ÷ weekly loss

For the same 80 kg person with a TDEE of 2,600 kcal:

Picking a pace

A review on contest prep for natural bodybuilders suggests losing about 0.5 to 1% of body weight a week to keep as much muscle as possible (Helms, Aragon & Fitschen, 2014). In a study with elite athletes who kept lifting four times a week, the group losing 0.7% a week gained lean mass and lost more fat than the group aiming for 1.4% a week, whose lean mass didn't change (Garthe et al., 2011). Many people also find a slower pace easier to stick with.

There is also a floor. A common guideline is not to go below about 1,200 kcal a day for women or 1,500 for men unless a health professional is supervising (Harvard Health). If your target lands under that, the calculator warns you; pick a slower pace or move more instead.

Why the goal date is optimistic

The 7,700 kcal per kg figure is the metric version of the old 3,500 kcal per pound rule. It treats every kilo you lose as the same mix of tissue. A modelling paper showed that the energy in a lost kilo depends on how much body fat you start with: the rule roughly fits people with more than 30 kg of fat and overstates the deficit needed per kilo in leaner people, who lose a bigger share of lean tissue (Hall, 2008).

Your body also adapts. As you get lighter, you burn less, so the same intake produces a smaller deficit week after week. A later model put the half time of weight change after a change in intake at about a year (Hall et al., 2011). The straight line in this calculator ignores that, so treat the date as a best case.

How to use it

• Weigh yourself a few mornings a week and compare weekly averages. Water and food in your gut can move single readings by a kilo or more.
• Every 4 to 5 kg lost, recalculate your TDEE with your new weight and update your target.
• Keep protein high and keep lifting to hold on to muscle while you lose fat.

This page is general information, not medical advice. If you are pregnant or breastfeeding, under 18, have a medical condition or have had an eating disorder, don't diet without help from a doctor or a registered dietitian.