Calorie Deficit Calculator
Estimate weight change from the gap between maintenance calories (TDEE) and daily intake. Explains the 3,500 kcal rule, its limits and safe-use cautions.
Results
Daily deficit / surplus
Est. weekly change
- Est. ~30-day change
- 4.29 lb (1.94 kg)
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Educational estimates · not financial advice · free, no signup
Formula / how it works
≈3500 kcal ≈ 1 lb body energy store (rough). Weekly lb ≈ (TDEE−intake)×7/3500.
Detailed guide
What it is, how to use it, how to read the numbers, common mistakes, a worked example, formulas, and FAQs.
What this calculator is
Body weight changes when the energy you eat differs from the energy you use. If your maintenance calories, also called total daily energy expenditure, are 2,400 and you eat 1,900, you have a 500 kcal daily deficit. Using the traditional estimate that roughly 3,500 kcal corresponds to a pound of body weight, that deficit would lead to about a pound lost per week. This calculator applies that arithmetic to your numbers. It is a planning aid, not a prediction. Water balance, muscle, metabolic adaptation and measurement error mean that real changes differ and usually slow over time. Very low intakes should only be undertaken under medical supervision, and people who are pregnant, underweight, young or managing a medical condition should seek professional advice.
When to use / who it helps
- You know your estimated maintenance calories and want to see what an intake target implies.
- You want to translate a daily deficit into weekly and monthly changes.
- You are comparing a modest and an aggressive plan.
- You are talking to a dietitian and want numbers to discuss.
- You want to see how adding exercise changes the net gap.
How to use
Steps
- Estimate your TDEE with the TDEE or BMR calculator.
- Enter your maintenance calories per day.
- Enter the daily intake you are considering.
- Read the daily deficit or surplus.
- Read the estimated weekly and 30-day change.
- Re-check your weight every few weeks and adjust the estimate.
How to interpret results
- A positive number means a deficit and expected loss; a surplus would suggest gain.
- The 3,500 kcal rule is an approximation that tends to overstate long-term loss as the body adapts.
- Early changes often include water, so initial results can look larger.
- A larger deficit is not automatically better; muscle loss, fatigue and nutrient gaps are risks.
- Individuals vary widely, so use the results as a starting point.
Common mistakes & gotchas
- Using a TDEE that is too high for your actual activity.
- Cutting intake too low to speed up results.
- Expecting linear loss indefinitely.
- Ignoring non-scale progress and health markers.
- Applying adult estimates to children, pregnancy or medical conditions.
Worked example
Worked example — TDEE 2,400, intake 1,900
- Daily deficit: 2,400 − 1,900 = 500 kcal.
- Weekly deficit: 500 × 7 = 3,500 kcal.
- Estimated weekly loss: 3,500 ÷ 3,500 = 1 lb (about 0.45 kg).
- Over 30 days: 500 × 30 = 15,000 kcal ÷ 3,500 ≈ 4.29 lb (1.94 kg).
Result: About 1 lb a week and roughly 4.3 lb over 30 days, with real results likely to slow.
To load the form's own demo values, tap Try example above the Calculate button.
How to calculate / formula
≈3500 kcal ≈ 1 lb body energy store (rough). Weekly lb ≈ (TDEE−intake)×7/3500.
Frequently asked questions
How many calories in a pound of fat?
The rule of thumb is about 3,500 kcal, though the true value varies and net weight change is more complex.
Is a 500 kcal deficit safe?
Many guidelines consider a moderate deficit reasonable for many adults, but suitability depends on health, body size and goals. Check with a professional.
Why did I lose less than predicted?
Metabolism adapts, TDEE estimates are imperfect, and food tracking has errors.
Does exercise count?
Yes, it raises TDEE, and so increases the deficit for the same intake.
What is TDEE?
Total daily energy expenditure: the calories you burn per day including activity.
Can I use this to gain weight?
A negative deficit, a surplus, indicates expected gain at the same rough rate.
For education and personal goal-setting only — not medical advice, diagnosis, or treatment. Talk to a qualified clinician about your health. Full disclaimer