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Calorie deficit calculator

Estimate maintenance calories, choose a daily gap, and get a starting target plus a projected date for your goal weight, with the formula and its limits shown clearly.

Tell us the basics

Select a measurement. Adjust the tape.

WeightSet your measurement

Illustrative figure · your measurements drive the estimate

Add one and the result projects a finish date at your chosen gap.

Sex used by the equation

Mifflin–St Jeor uses different constants for female and male bodies. Choose the one that best fits the equation you want to use.

Usual activity level

Desk-based day with little planned exercise

Daily calorie gap

No signup. Your measurements stay in this browser and are not included in analytics.

Your result

Estimate only

Your daily calorie estimate

We’ll estimate resting needs, maintenance calories, and a starting target. The result is rounded to avoid false precision.

Maintenance and target shown separately

Low and inappropriate targets are blocked

Formula and assumptions explained below

For adults 18+ who are not pregnant or breastfeeding. This is an estimate, not medical advice or a meal plan. The calculator blocks underweight-screening results and uses conservative self-guided floors of 1,200 calories for the female equation and 1,500 for the male equation; individualized needs can still be higher.

How to calculate your calorie deficit

The result combines a published resting-energy equation with a simplified activity estimate, then turns the gap into time. Each step adds uncertainty, so the final numbers are deliberately rounded.

  1. 01

    Estimate resting energy

    Mifflin–St Jeor estimates resting energy expenditure from age, height, weight, and a female or male equation constant. The original study included 498 healthy adults aged 19–78.

  2. 02

    Estimate maintenance calories

    The resting estimate is multiplied by the activity level you choose. Daily movement varies substantially, so maintenance is better understood as a starting estimate than a measured burn.

  3. 03

    Subtract the chosen gap

    The calculator subtracts 250, 500, or 750 calories, checks whether the result is appropriate for a self-guided estimate, and rounds to the nearest 50 calories to avoid false precision.

  4. 04

    Project a finish date

    If you enter a goal weight, the calculator divides the weight you want to lose by the daily gap, using about 7,700 calories per kilogram (3,500 per pound), and counts forward from today. The shortcut ignores the way energy needs fall as you lose weight, so the real date tends to land later, not earlier.

A starting point, not a promise

Maintenance calories are the estimated intake that would keep weight roughly stable at the selected activity level. The target is that estimate minus your chosen daily gap, and the projected date assumes that gap holds every day until you arrive.

Real weight change is not perfectly linear. Metabolism, activity, food measurement, water balance, sleep, health conditions, and medication can all move the result. The CDC describes gradual loss of roughly one to two pounds per week as more likely to be maintained, but that population guidance is not an individual guarantee.

If you use the estimate, compare it with several weeks of real-world trend rather than reacting to one day. If you feel unwell, have a clinician-directed nutrition plan, or are unsure whether a deficit is appropriate, use qualified individual guidance instead.

Use the right tool for the question

A calorie-deficit estimate answers “where could I start, and roughly when would I arrive?” If you are choosing the goal itself or checking progress, use the more specific tool.

Browse all free tools
Ideal Weight CalculatorA reference range for your height, if you are still choosing a goal weight.Weight Loss Percentage CalculatorThe percent of starting weight lost, and the 5 and 10 percent marks.

Frequently asked questions

How do I calculate my calorie deficit by hand?

Start with resting energy from Mifflin–St Jeor: 10 times your weight in kilograms, plus 6.25 times your height in centimeters, minus 5 times your age, then add 5 for the male equation or subtract 161 for the female one. Multiply by an activity factor between 1.2 and 1.725 to estimate maintenance. Subtract a gap you can live with, usually 250 to 750 calories, and that is your daily target. To turn the gap into time, divide the weight you want to lose by the gap using about 7,700 calories per kilogram, or 3,500 per pound.

How long does it take to lose 20 pounds?

With the 3,500-calories-per-pound shortcut, a 500-calorie daily gap puts 20 pounds at about 20 weeks. A 750-calorie gap shortens that to around 13 weeks, and a 250-calorie gap stretches it past nine months. Enter your goal weight above and the calculator projects a date from your own numbers. Treat it as a planning horizon: loss usually slows as you get lighter, and a week of travel or illness moves the date without meaning anything went wrong.

Is a 1,000-calorie deficit too much?

For most people, yes, at least as a self-guided starting point. A 1,000-calorie gap is the textbook route to two pounds a week, but for many adults it lands below the 1,200 or 1,500 calorie floors this calculator uses, which is why it is not one of the options here. Larger gaps also tend to cost muscle, sleep, and training quality, and they are harder to keep up for the months a meaningful goal takes. If your maintenance estimate is high enough that 1,000 still leaves a comfortable intake, that is a conversation for a clinician or dietitian, not a calculator.

What deficit do I need to lose 2 pounds a week?

Roughly 1,000 calories a day under maintenance, using the 3,500-calorie shortcut. The CDC describes one to two pounds a week as the gradual range people tend to keep off, and two is the top of it. Most people find one pound a week, from a 500-calorie gap, far easier to sustain. The projected date in the result shows what each option costs you in time, so you can pick the trade you can actually hold.

What calorie deficit should I choose?

A smaller gap is usually the better place to start. This calculator offers 250, 500, and 750 calories per day, then checks the result against your estimated maintenance needs. A higher option is not automatically better, and the calculator blocks combinations that produce an inappropriately low self-guided target.

Is a 500-calorie deficit always one pound per week?

No. The familiar 3,500-calorie rule is a rough shortcut, not a promise. Energy expenditure changes over time, and sleep, activity, medication, health conditions, food measurement, and normal water shifts can all affect what you observe.

How accurate is this calorie deficit calculator?

It is a starting estimate. Mifflin–St Jeor predicts resting energy expenditure from age, height, weight, and a sex-specific constant. An activity multiplier introduces more uncertainty, so the result is rounded to the nearest 50 calories rather than presented as an exact prescription. The projected date inherits all of that uncertainty and adds the assumption that the gap holds every day.

Who should not use this calculator?

It is intended for adults 18 and older who are not pregnant or breastfeeding. It is not appropriate for children, for anyone whose measurements fall below the adult BMI screening range, or when a clinician has prescribed a nutrition target. People with an eating-disorder history, significant medical conditions, or medicines that affect weight or appetite should use individualized professional guidance.

Sources and further reading

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