Calorie Deficit Calculator
Work out the deficit you need to hit a weight loss goal by a target date.
Please note: For general information only. This is not medical advice — speak to a doctor or registered dietitian before changing your diet, training or medication.
What the Calorie Deficit Calculator does
A calorie deficit means eating less than you burn. Since about 7,700 calories corresponds to a kilogram of body mass, dividing your total goal by your timeline gives the daily deficit required — and shows immediately whether the timeline is realistic.
Formula
Total deficit = Weight to lose (kg) × 7,700Daily deficit = Total deficit ÷ (Weeks × 7)Target calories = TDEE − Daily deficit
Inputs explained
| Input | Unit | Required | Notes |
|---|---|---|---|
| Units | one of 2 options | Yes | — |
| Current weight | kg or lb | Yes | Accepts 1 or more. |
| Goal weight | kg or lb | Yes | Accepts 1 or more. |
| Weeks to reach the goal | number | Yes | Accepts 1 or more, up to 260. |
| Your maintenance calories (TDEE) | cal | Optional | Accepts 800 or more. |
How to use it
- Choose Units.
- Enter Current weight, Goal weight and Weeks to reach the goal.
- Optionally add Your maintenance calories (TDEE).
- Select Calculate.
Worked example
Losing 10 kg in 20 weeks with a 2,600 calorie maintenance.
- Current
- 90
- Goal
- 80
- Weeks
- 20
- TDEE
- 2600
0.5 kg a week, a 550 calorie daily deficit, so eat about 2,050 calories.
Frequently asked questions
Why has my weight loss stalled?
As you get lighter, your maintenance calories fall, so the original deficit shrinks. Water retention also masks fat loss for weeks at a time. Recalculate TDEE every 5 kg.
Can I lose fat faster with a bigger deficit?
Up to a point. Beyond roughly 25% below maintenance, an increasing share of the loss comes from muscle and adherence collapses.
Method and sources
Method. A total deficit is derived from the weight to lose using the long-standing conversion of roughly 7,700 kcal per kilogram, then divided across the timeline to give a daily figure.
Assumptions
- The energy-per-kilogram conversion holds throughout, and maintenance calories stay constant across the period.
- Losses come predominantly from fat rather than lean tissue, which depends on protein intake and resistance training that this does not model.
Limitations
- The 7,700 kcal per kilogram rule descends from a 1958 estimate of the energy in a pound of adipose tissue and is known to overpredict real loss. Expenditure falls as weight falls, so a constant deficit yields progressively less, and actual loss flattens well short of the straight line this projects.
- Early loss runs ahead of the line — mostly glycogen and its associated water — which makes the rule look accurate for a fortnight and optimistic thereafter.
- A daily deficit that arithmetic says is achievable can still be too aggressive to be safe or sustainable. Very low intakes warrant clinical supervision.
Sources
- Caloric equivalents of gained or lost weight — The American Journal of Clinical Nutrition 6(5):542–546 (Max Wishnofsky), 1958. The origin of the energy-per-unit-mass conversion used, and by extension the reason it is a rule of thumb rather than a law.