Health & Wellbeing2 min check

Weight Loss Calculator

Work out the calorie deficit you'd need to reach a target weight by a target date — and whether the timeline is realistic.

Short answer

1 kg of fat ≈ 7,700 kcal. To lose 0.5 kg per week you need a ~3,850 kcal weekly deficit (about 550 kcal/day). NHS recommends a max sustainable rate of 0.5–1 kg/week.

Step 1 of 10%

Calculation method, coverage and version

Inputs used: Current weight (kg), Target weight (kg), Weeks to reach it, Your TDEE (use Calorie Calculator).
Calculation approach: The calculator applies the rules and assumptions described in “How it works” to the values you enter. Rounding can cause small differences from an official or provider calculation.
Coverage: Health & Wellbeing. UK nations, tax treatment, local rules and provider criteria can differ; check the official sources shown below before acting.
Content version: No page-specific review date is currently published. Treat the result as indicative and verify current rules independently.

Not included unless explicitly requested: personal circumstances not entered, provider discretion, future rule changes, professional fees and case-specific exceptions. Read the full calculator methodology.

How it works

Each kg of fat stores ~7,700 kcal. Multiply your weekly target loss by 7,700 to get the weekly calorie deficit, divide by 7 for daily. Subtract from your TDEE to get your daily eating target.

Worked example

85 kg → 75 kg in 20 weeks (TDEE 2,200):

10 kg ÷ 20 = 0.5 kg/week (safe)
3,850 ÷ 7 = 550 kcal/day deficit
2,200 − 550 = 1,650 kcal/day target

Who should use this

•Anyone planning a weight-loss target
•People wanting realistic timelines
•Pre-bariatric or weight-management programme participants

Common mistakes

×Setting too aggressive a timeline (1 kg/week+)
×Forgetting to recalculate as you lose weight (TDEE drops too)
×Crash dieting — loses muscle and rebounds quickly
×Skipping strength training — keeps fat-loss but loses muscle

Frequently asked questions

How fast can I safely lose weight?▾

0.5-1 kg per week is the NHS recommendation. Faster is rarely sustainable and risks muscle loss.

Why have I plateaued?▾

Your TDEE drops as you lose weight (lower mass to maintain) plus 'adaptive thermogenesis'. Re-calculate every 4-6 kg lost.

Should I exercise to create the deficit or eat less?▾

Both work. Exercise (especially strength) preserves muscle, but most of the deficit usually comes from food — it's easier to eat 500 fewer kcal than burn 500.

Is fasting better?▾

Intermittent fasting is one approach to eating in a deficit; total calories matter most. Time-restricted eating helps some people stick to a deficit.

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Calorie Calculator →BMI Calculator →Ideal Weight Calculator →Water Intake Calculator →