Weight loss date calculator
If you hold a steady calorie deficit, you can estimate the date you reach your goal weight. One kilogram of body fat stores roughly 7,700 calories, so a 500-calorie daily deficit loses about half a kilogram a week. FitCalcs turns your current weight, target weight and chosen deficit into an estimated finish date. It is a straight-line model, so loss slows as you get lighter: treat the date as a best case and re-check it. This is general information, not personalised dietary advice.
How this is worked out
One kilogram of body fat stores roughly 7,700 kcal, so the time to lose a given amount is the total energy gap divided by your daily deficit:
weeks = (weight to lose kg x 7700) ÷ (daily deficit x 7)
This is a straight-line model. In reality weight loss slows as you get lighter, because a smaller body burns fewer calories, so treat the date as a best case and re-check your numbers every few weeks. The NHS suggests a steady 0.5 to 1 kg a week as safe and sustainable.
Informational only, not medical or dietary advice. Editorially reviewed by FitCalcs, with each figure citing its source.
Common questions
How is my weight loss date estimated?
From your calorie deficit. One kilogram of body fat stores roughly 7,700 calories, so FitCalcs turns your daily deficit into a weekly rate of loss, then projects your current weight down to your target to estimate a finish date. It is a straight-line model, so treat the date as a best case. This is general information, not personalised dietary advice.
How fast is it safe to lose weight?
A modest deficit is the sensible route. Cutting around 500 to 600 calories a day takes off roughly half a kilogram a week, the pace the NHS calls safe and sustainable. Faster loss is harder to hold and tends to cost more muscle. The calculator caps the rate so the date reflects a sensible pace rather than a crash diet.
Why does my rate of loss slow down over time?
Because a lighter body burns fewer calories, so the same eating pattern becomes a smaller deficit as you go. This calculator uses a straight-line estimate, which does not model that slowdown, so real loss usually lags the projection later on. Re-check your numbers every few weeks and adjust rather than trusting one fixed date.
Is a very aggressive deficit safe?
No, not on your own. NICE classes diets of around 800 calories a day or fewer as very-low-energy diets and says they should only be used under medical or dietetic supervision, because unsupervised they risk nutrient deficiencies, gallstones and electrolyte problems. Aim for a modest deficit instead, and speak to a GP or registered dietitian before anything drastic.
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Editor, FitCalcs
Oliver Mackman is the named editor of FitCalcs and a director of Best Business Loans Ltd (Companies House 16833937), the company that operates the site. He is accountable for its editorial standards, sourcing and corrections, and requires every result to cite the underlying equation and the named UK source behind it, with health tools carrying the appropriate not-medical-advice caveats.
Last reviewed: 12 June 2026