FitCalc

Weight Loss Calculator

How long it will take to reach your goal weight at a chosen rate of loss.

Quick answer: Weight loss time = weight to lose × 3,500 kcal ÷ daily deficit. To lose 20 lb at a 500 kcal daily deficit: 20 × 3,500 ÷ 500 = 140 days, or about 20 weeks. The calculator also shows the alternative if you choose a target date.

lb
lb
lb/week

0.25–1 kg (0.5–2 lb) per week is a common range.

days

Used to work out the daily deficit needed.

Weight to lose
30.0 lb
Daily deficit at target rate
500 kcal
Deficit for your date
1,250 kcal/day
Estimated time
30.0 weeks
Start → goal200 → 170 lb
Total deficit105,000 kcal
At chosen rate1 lb/week
Projected goal dateApr 16, 2027
Required daily deficit for your date1,250 kcal

The 3,500 kcal ≈ 1 lb rule is an approximation; real weight loss is not perfectly linear as the body adjusts. A deficit of 0.5–1% of body weight per week is generally sustainable. Severely restricting calories can cost muscle and rebound — choose a rate you can hold.

Core facts
Rule3,500 kcal ≈ 1 lb of fat
Common rate0.5–1 kg (1–2 lb) per week
OutputTime to goal + daily deficit
AlsoDeficit needed for a fixed date

What is Weight Loss Calculator?

This calculator turns a goal weight into a timeframe. Enter your starting weight, goal weight and the rate at which you want to lose, and it computes the daily calorie deficit and the number of weeks needed. Alternatively, enter a target date and it works backwards to the deficit you would need to hit it. The arithmetic rests on the approximation that a pound of fat holds about 3,500 kcal. Real life is less tidy: early loss includes water, loss slows as you get lighter, and adherence varies week to week. Use the result as a planning estimate, and set a rate of 0.5–1% of body weight per week to keep the plan sustainable and protect muscle.

Common Uses for Weight Loss Calculator

  • Turn a goal weight into a realistic timeline
  • See what daily deficit a target date requires
  • Compare losing faster versus slower
  • Plan checkpoints for a longer fat-loss phase

Frequently Asked Questions

How long does it take to lose weight?
At a 500 kcal daily deficit, roughly 1 lb (0.45 kg) per week. Losing 10 kg therefore takes about 22 weeks at that rate. The calculator gives the exact figure for your numbers.
Is 2 lb a week too fast?
It depends on starting weight. Losing more than about 1% of body weight per week tends to cost muscle and is hard to sustain; for most people 0.5–1% per week is the sweet spot.
Why is my real weight loss slower than predicted?
The 3,500 kcal rule is an approximation, maintenance falls as you lose weight, and water retention can mask fat loss for a week or two. Adjust intake based on real trends rather than the formula alone.
Should I include exercise in the timeline?
The deficit can come from food, activity or both. Adding activity increases the deficit without cutting food further, which often makes a plan easier to stick to.

More Weight Management Calculators

Weight Loss Goal Date Calculator
Pick a goal date and see the daily deficit and weekly rate it requires.
Goal Weight Calculator
Find a healthy goal weight from your height, then see the timeline to reach it.
Weight Loss Percentage Calculator
How much of your starting weight you have lost, as a percentage.
Calories in a Pound of Fat
Why a pound of fat is treated as 3,500 kcal, and what a deficit really produces.
Intermittent Fasting Calculator
Eating window and fasting schedule for 16:8, 18:6, 20:4 and 14:10 plans.

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