BYTETOOLS

Calorie Deficit Calculator

Work out the daily calorie deficit and intake target needed to reach a goal weight by a chosen date, with a safe intake floor and a weekly loss rate check.

Your daily target

1,583 kcal/day

That is a 917 kcal deficit against 2,500 kcal of maintenance, which works out at about 0.83 kg lost per week.

10.0 kg × 7,700 kcal ÷ 84 days = 917 kcal/day

10.0
Weight to lose (kg)
917 kcal
Daily deficit
1,583 kcal
Target intake
0.83 kg
Loss per week

This plan loses 0.93% of your body weight per week, which sits inside the commonly recommended 0.5–1% band.

Projected weight over time

WeekProjected weight (kg)Lost so far (kg)
189.20.8
288.31.7
387.52.5
486.73.3
585.84.2
685.05.0
784.25.8
883.36.7
982.57.5
1081.78.3
1180.89.2
1280.010.0

Straight-line projection at a constant deficit. Real weight loss is lumpier: water shifts, glycogen and digestive contents move the scale by a kilo or two day to day, and metabolic adaptation typically slows the rate after the first few weeks.

Estimates only — this is arithmetic, not medical advice, and it does not diagnose anything. The 3,500 kcal per pound (7,700 kcal/kg) rule comes from Wishnofsky's 1958 paper and assumes every pound lost is pure fat; researchers including Kevin Hall have shown it overstates long-run loss because TDEE falls as you get lighter. Do not use a very low intake without medical supervision, and speak to a doctor or dietitian before starting a deficit if you are pregnant, breastfeeding, under 18, or managing diabetes or an eating disorder.

What is the Calorie Deficit Calculator?

A calorie deficit calculator multiplies the weight you want to lose by the energy stored in each unit of body mass (about 7,700 kcal per kilogram or 3,500 per pound), divides by the days you have, and subtracts the result from your maintenance calories to give a daily intake target.

  • Daily deficit and target intake from a goal weight plus either a week count or a calendar date
  • Editable energy density — 7,700 kcal/kg and 3,500 kcal/lb are the defaults, not hardcoded
  • Configurable minimum intake floor, with a recalculated timeline when the floor caps your deficit
  • Warning when the plan loses more than 1% of body weight per week
  • Week-by-week projected weight table down to your goal
  • Runs entirely offline in your browser — no weights or calories leave your device

How to use the Calorie Deficit Calculator

  1. 1

    Pick kilograms or pounds, then enter your current weight, your goal weight and your maintenance calories (TDEE).

  2. 2

    Choose whether to set the timeframe as a number of weeks or as a target date, and fill in that field.

  3. 3

    Adjust the calories-per-unit-of-body-weight figure and the minimum intake floor if your plan uses different assumptions.

  4. 4

    Read the daily target, the deficit it implies and the weekly loss rate in the four summary tiles.

  5. 5

    Check the projected weight table and any amber warnings about the intake floor or a loss rate above 1% per week.

About the Calorie Deficit Calculator

The ByteTools Calorie Deficit Calculator turns a goal weight and a deadline into one number you can actually act on: how many calories to eat each day. Enter your current weight, your goal weight, how long you want to take and your maintenance calories, and it shows the daily deficit that plan requires and the intake target it leaves you.

It also tells you when the plan is unrealistic. A configurable intake floor stops it recommending a starvation diet, and if your timeframe would push you below that floor the tool recalculates how long the goal will really take. A separate warning fires when the plan loses more than about 1% of your body weight a week, which is the point most guidance considers too fast to sustain.

Everything runs in your browser with JavaScript. Nothing you type is uploaded, logged or stored on a server, so your weight and calorie figures stay on your device. These are estimates for planning only — not medical advice, and not a diagnosis of anything. Talk to a doctor or a registered dietitian before starting any significant deficit.

Frequently asked questions

How big a calorie deficit do I need to lose 1 kg a week?

Using the standard 7,700 kcal per kilogram figure, losing 1 kg a week needs a deficit of about 1,100 kcal a day. That is a large deficit for most people, and it is only realistic if your maintenance calories are high enough that you still eat a sensible amount. Enter your own numbers above and the tool will show whether the intake it implies is above your floor.

Is 3,500 calories per pound accurate?

It is a useful rule of thumb, not a law. The figure comes from Max Wishnofsky's 1958 paper and assumes every pound lost is pure fat. In practice your maintenance calories fall as you get lighter, so a fixed deficit produces less and less loss over time — research from Kevin Hall's group at the NIH shows a steady deficit tends to plateau rather than continuing in a straight line.

What is a safe rate of weight loss?

Most guidance points to roughly 0.5 to 1% of body weight per week. Faster than that and a larger share of the loss comes from muscle and water rather than fat, and the diet becomes much harder to stick to. This calculator flags any plan above 1% per week so you can lengthen the timeframe instead.

How low should my calorie intake go?

Common floors are around 1,200 kcal a day for women and 1,500 for men, which is why the tool defaults to a floor you can edit. Very low calorie diets below that do exist, but they are meant to be medically supervised, not self-prescribed. If your goal needs a deficit that breaks the floor, take longer rather than eating less.

Do I need to know my TDEE first?

Yes — the deficit is subtracted from your maintenance calories, so you need a reasonable estimate of them. A TDEE or BMR calculator will give you a starting figure from your height, weight, age and activity level, and two or three weeks of weighing yourself will tell you how far off it was.

Is anything I type here sent anywhere?

No. Every calculation happens in JavaScript inside your browser. Your weights, calories and dates are never transmitted or saved to a server, and the page works offline once it has loaded.

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