Calorie Deficit Calculator
Turn a weight-loss goal into a daily calorie deficit, a target intake, and a realistic timeline. Enter your maintenance calories directly, or let the tool estimate them from your age, sex, height, weight, and activity using the Mifflin-St Jeor equation. Add a goal weight to see how many weeks it takes and the date you would reach it.
Formula
Worked example
A 30-year-old man, 178 cm and 82 kg, moderately active: BMR ≈ 1,791 kcal, TDEE ≈ 1,791 × 1.55 ≈ 2,776 kcal/day. To lose 0.5 kg/week the daily deficit is 0.5 × 7,700 ÷ 7 ≈ 550 kcal, so target intake ≈ 2,226 kcal/day. To reach a 75 kg goal (7 kg to lose) takes about 14 weeks.
How a calorie deficit drives weight loss
Your body draws on stored energy when you eat fewer calories than you burn, this gap is the calorie deficit. Roughly 7,700 kilocalories are stored in each kilogram of body fat (about 3,500 kcal per pound), so to lose weight at a chosen rate you multiply that rate by this energy density to find the weekly deficit, then divide by seven for a daily figure. Subtracting the daily deficit from your maintenance calories (your total daily energy expenditure, or TDEE) gives the intake to aim for. This calculator runs that arithmetic for you in either metric or imperial units.
Estimating your maintenance calories
If you do not already know your TDEE, switch to the estimate mode and enter your sex, age, height, weight, and activity level. The tool first finds your basal metabolic rate (BMR), the energy you burn at complete rest, using the Mifflin-St Jeor equation, which research considers one of the most accurate predictive formulas. It then multiplies BMR by an activity factor: about 1.2 for sedentary, 1.375 for lightly active, 1.55 for moderately active, 1.725 for very active, and 1.9 for athletes or those with a physical job. That product is your maintenance number, the starting point for any deficit. If you prefer, switch to manual mode and type a TDEE you trust from a tracking app or your own logging.
Setting a goal weight and timeline
Add an optional goal weight to turn the deficit into a plan with a finish line. The calculator divides the total amount you want to lose by your chosen weekly rate to estimate the number of weeks, then projects a target date and draws the expected weight curve week by week. Use this to sanity-check whether your rate is realistic for the deadline you have in mind, and to see when slowing down would still get you there in time. Remember that the line is a straight-line estimate; real progress wobbles around it.
Choosing a safe and sustainable rate
Most health authorities, including the CDC, suggest losing about 0.5 to 1 kilogram (1 to 2 pounds) per week as a realistic and durable pace. Larger deficits speed results but are harder to maintain, can erode muscle, and may leave you short on nutrients. A common floor is not eating below roughly 1,200 kcal a day for women or 1,500 for men without medical supervision. If your target intake drops below those levels, pick a slower weekly rate or increase your activity so the deficit comes partly from movement rather than food restriction alone.
Why real-world results vary
The 7,700-kcal-per-kilogram rule is a useful planning estimate, not a guarantee. Actual loss depends on water balance, glycogen and sodium shifts, hormonal changes, and the fact that your maintenance calories fall as you lose weight, a phenomenon called metabolic adaptation. Early weeks often show faster scale movement from water loss, while later weeks slow down. Because of this, weigh trends over several weeks rather than reacting to a single day, and recalculate your maintenance calories as your weight changes to keep the deficit accurate.
Weekly loss vs. daily deficit
| Weekly loss | Daily deficit | Pace |
|---|---|---|
| 0.25 kg (0.5 lb) | ~275 kcal | Gentle |
| 0.5 kg (1 lb) | ~550 kcal | Healthy |
| 0.75 kg (1.5 lb) | ~825 kcal | Moderate |
| 1 kg (2 lb) | ~1,100 kcal | Aggressive |
How a weekly weight-loss target maps to the daily calorie deficit it requires, using 7,700 kcal per kg (3,500 kcal per lb). Faster rates need larger deficits and may be harder to sustain.
Frequently asked questions
How big should my calorie deficit be?
A deficit of about 500 kcal a day produces roughly 0.45 kg (1 lb) of loss per week, which most guidelines treat as safe and sustainable. Deficits above 1,000 kcal a day are aggressive and harder to maintain. Avoid dropping intake below about 1,200 kcal/day (women) or 1,500 kcal/day (men) without medical supervision.
How does the calculator estimate my maintenance calories?
In estimate mode it computes your basal metabolic rate from your sex, age, height, and weight using the Mifflin-St Jeor equation, then multiplies by an activity factor (1.2 sedentary up to 1.9 very active) to get your total daily energy expenditure (TDEE). That TDEE is your maintenance number. In manual mode you simply enter a TDEE you already know.
How long will it take to reach my goal weight?
Enter a goal weight below your current weight and the calculator divides the amount to lose by your weekly rate to estimate the number of weeks and a target date. For example, losing 7 kg at 0.5 kg per week takes about 14 weeks. Real progress is rarely a straight line, so treat the date as a planning estimate.
Does this calculator replace medical advice?
No. It provides general estimates for healthy adults based on standard formulas and an energy-density rule. Weight-loss needs differ with age, health conditions, pregnancy, and medications. Talk to a doctor or registered dietitian before starting a significant calorie deficit, especially if you have a medical condition.