Calorie Deficit Calculator
Set a goal weight and target date, and see the daily calorie deficit — and daily intake — it takes to get there, with a safety check on the pace.
The deficit math
Daily deficit = Total deficit ÷ (weeks × 7)
Daily intake = Maintenance − Daily deficit
Lose 15 lb in 12 weeks on 2,200 maintenance:
15 × 3,500 = 52,500 cal ÷ 84 days = 625/day deficit → eat ~1,575 cal/day. That's a healthy ~1.25 lb/week pace.
Lose 10 kg in just 6 weeks, from a 90 kg starting weight, on 2,000 maintenance calories:
10 × 7,700 = 77,000 cal ÷ 42 days = 1,833 cal/day deficit → target intake = 2,000 − 1,833 ≈ 167 cal/day. That's far below the roughly 1,200-calorie floor this calculator flags, and the weekly rate — 10 ÷ 6 ≈ 1.67 kg/week, about 1.85% of body weight — also exceeds the recommended 1% ceiling.
The fix isn't a more aggressive diet; it's a longer timeframe. Stretching the same 10 kg loss to 15-16 weeks instead of 6 would bring the daily deficit down to a sustainable range similar to the first example above.
Keeping the deficit sustainable
The best deficit is the one you can actually hold. If the calculator asks you to eat uncomfortably little, extend the timeframe rather than white-knuckling it — slow, steady loss keeps more muscle and rebounds less. Aim to keep the rate under about 1% of body weight per week. Protect muscle with adequate protein and resistance training, and recalculate as you lighten (your maintenance drops, so the same intake becomes a smaller deficit). Track honestly — under-logging is the most common reason a "deficit" doesn't produce loss. Guide: How many calories to lose weight?
Weekly loss rate by deficit size
| Daily deficit | Weekly loss (lb) | Weekly loss (kg) |
|---|---|---|
| 250 cal | 0.5 lb | 0.23 kg |
| 500 cal | 1.0 lb | 0.45 kg |
| 750 cal | 1.5 lb | 0.68 kg |
| 1,000 cal | 2.0 lb | 0.91 kg |
This is the same 3,500-cal-per-pound approximation applied at a few common deficit sizes, so you can see at a glance what a given daily number implies over a week without doing the arithmetic yourself.
Common calorie-deficit mistakes
- Treating 3,500 cal/lb as an exact biological constant. It's a useful approximation that drifts further from reality over longer timeframes and larger total losses, as noted in the FAQ below.
- Keeping the same daily intake as weight drops. Maintenance calories fall along with body weight, so a fixed intake becomes a smaller deficit over time — recalculate every 10-15 lb.
- Compressing the timeframe until the plan demands under ~1,200 cal/day. As the aggressive-timeframe example above shows, the better fix is a longer timeframe, not a more severe deficit.
Frequently asked questions
What is a calorie deficit?
Eating fewer calories than you burn, so the body uses stored fat. It's the requirement for weight loss.
How big should my deficit be?
300–500/day (0.5–1 lb/week) suits most people; over 1,000/day is hard to sustain.
Why did my weight loss stall?
A lighter body burns less, shrinking the deficit — plus water and tracking noise. Recalculate every 10–15 lb.
What if my timeframe requires eating too little?
The calculator flags a target under roughly 1,200 cal/day as too aggressive — extending the timeframe is the better fix, as shown in the worked example above.
Does the 3,500-cal-per-pound rule get less accurate over time?
Yes — it's an approximation that drifts further from reality for larger total losses or longer timeframes, which is why recalculating every 10-15 lb matters.
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Medical disclaimer: The 3,500-cal-per-pound rule is a useful approximation, not an exact biological law. This is educational, not medical or nutritional advice. Consult a professional before restrictive dieting. Last reviewed: September 2026.