Calorie Deficit Calculator

A deficit of 550 calories a day is roughly half a kilogram of loss a week; 1,100 is roughly a kilogram. Give it your stats and either a deficit or a target date, and it prints the daily calorie figure, the weekly rate, and the week it lands. Intake is floored at 1,200 calories whatever you ask for.

Sex

Age: 30 years

Height

centimeters

Current Weight

kilograms

Goal Weight

kilograms

Activity Level

Approach

Daily deficit: 500 kcal/day

200 kcal 1000 kcal

How this is calculated

Maintenance calories first, then the subtraction. Resting rate comes from Mifflin-St Jeor — 10 × weight in kilograms + 6.25 × height in centimetres − 5 × age, then + 5 for men or − 161 for women — and is multiplied by one of the conventional activity factors: 1.2 sedentary, 1.375 lightly active, 1.55 moderately active, 1.725 very active, 1.9 extremely active.

The deficit is then either the one you pick or the one your target date implies. Given a date, the calculator works out the days between now and then, converts the weight you want to lose at roughly 7,700 calories per kilogram of body tissue, and divides. That conversion is a linear rule of thumb and it flatters long timelines: as you get smaller you burn less, so the real curve flattens and the last few kilograms take longer than the arithmetic says. The projection chart is drawn from the same straight line, which is why it is a plan rather than a forecast.

One floor is hard-coded and will not be crossed: daily intake never drops below 1,200 calories, whatever the date you typed asks for. If your target needs more than that, the calculator holds the floor and the timeline stretches instead.

Where this comes from

1. A new predictive equation for resting energy expenditure in healthy individuals — Mifflin et al., American Journal of Clinical Nutrition, 1990 (PubMed)
2. Body Weight Planner — National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), National Institutes of Health

Nothing on this site is medically reviewed — it cites its sources so you can check them. Read our editorial policy. Method last checked 21 August 2026.

A calorie deficit is the fundamental requirement for weight loss, but the size of that deficit matters enormously. Too small and progress stalls; too large and you risk muscle loss, fatigue, and metabolic slowdown that undermines your long-term results.

Intermittent fasting and calorie deficits work hand in hand. Fasting compresses your eating window, which for most people naturally reduces total intake. This calculator helps you find the sweet spot where fat loss is steady and sustainable.

Frequently Asked Questions

What is a safe calorie deficit for weight loss?

A deficit of 300-500 calories per day is considered safe and sustainable for most people, resulting in roughly 0.5 to 1 pound of fat loss per week. Larger deficits can lead to muscle loss, metabolic adaptation, and are harder to maintain long term.

Can a calorie deficit be too large?

Yes. Extreme deficits (over 1,000 calories per day) can cause muscle loss, hormonal disruption, nutrient deficiencies, and a significant drop in metabolic rate. This often leads to a rebound effect where weight is regained quickly once normal eating resumes.

Does intermittent fasting create a natural calorie deficit?

For many people, yes. By compressing your eating window, you tend to eat fewer total calories without consciously counting them. Studies show that most IF practitioners naturally reduce intake by 10-20%, which often puts them in a moderate deficit.

How do I break through a weight loss plateau?

Plateaus happen when your body adapts to your current deficit. Strategies include recalculating your TDEE at your new weight, slightly increasing activity, trying a different fasting protocol, incorporating refeed days, or adjusting your macronutrient ratios.

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Track your fasting progress in the Fasted app

The Fasted app tracks your fasting consistency and helps you maintain the routine that supports your calorie deficit naturally, without obsessive calorie counting.

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Calorie Deficit Calculator

High Deficit Warning

Projected Weight Loss

Fasting can help you get there