Calorie Deficit Calculator
How many calories should you eat to lose weight? Enter your stats and a weekly pace to get a daily calorie target and an estimated timeline to your goal weight.
Sex
These numbers look unusual. Please double-check your height and weight.
Estimates use the Mifflin-St Jeor formula and the common 7,700 kcal/kg rule of thumb; actual results vary with body composition, health, and genetics. Educational information only — not medical, nutrition, or fitness advice.
All calculations run in your browser — nothing is sent to a server.
How a calorie deficit actually works
Weight loss comes down to one relationship: eat fewer calories than your body burns in a day, and it draws on stored energy to cover the gap. This calculator finds your maintenance calories (TDEE) from your sex, age, height, weight and activity level using the Mifflin-St Jeor formula, then subtracts a deficit sized to the weekly pace you choose — mild, moderate, strong, or aggressive. The result is a single daily calorie number, plus an estimated timeline to your goal weight.
The formula behind the numbers
Basal metabolic rate (BMR) — the calories your body burns at complete rest — is estimated with the Mifflin-St Jeor equation:
- Men: BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age + 5
- Women: BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age − 161
BMR is then multiplied by an activity factor (1.2 sedentary to 1.9 extra active) to get TDEE — your true daily maintenance number. Your weekly pace is converted to a daily deficit using the common estimate that roughly 7,700 kcal equals 1 kg of body fat (about 3,500 kcal per pound), divided across 7 days. Subtracting that deficit from TDEE gives your daily calorie target.
Example 1 — a moderate cut. A moderately active 35-year-old woman, 165 cm and 70 kg, has a BMR near 1,393 kcal and a TDEE of roughly 2,160 kcal. Choosing a 0.5 kg/week pace subtracts about 550 kcal/day (0.5 × 7,700 ÷ 7), for a daily target near 1,610 kcal. To lose 10 kg she'd need roughly 20 weeks (about 4.6 months) at that pace.
Example 2 — a mild, sustainable cut. A moderately active 40-year-old man, 178 cm and 90 kg, has a TDEE near 2,740 kcal. A mild 0.25 kg/week pace subtracts about 275 kcal/day, landing at roughly 2,465 kcal — comfortably above the 1,500 kcal floor, and easier to stick to for months at a time than a steeper cut.
Example 3 — hitting the low-calorie floor. A lightly active 28-year-old woman, 158 cm and 55 kg, has a TDEE near 1,690 kcal. An aggressive 1 kg/week pace would subtract about 1,100 kcal/day, pushing the target near 590 kcal — well under the 1,200 kcal floor. This calculator flags that with a warning: at a small body size, the safer fix is a smaller weekly pace, not a lower calorie floor.
Choosing a weekly pace
| Pace | Daily deficit | Typical fit |
|---|---|---|
| 0.25 kg/week — mild | ≈ 275 kcal | Small deficit, easiest to sustain long-term |
| 0.5 kg/week — moderate | ≈ 550 kcal | Common, evidence-backed default for most people |
| 0.75 kg/week — strong | ≈ 825 kcal | Faster progress, more discipline required |
| 1 kg/week — aggressive | ≈ 1,100 kcal | Only realistic for people with a larger maintenance budget |
Faster is not always better: very large deficits increase the risk of muscle loss, fatigue, and rebound weight regain, and they are harder to hold for more than a few weeks. Slower, steadier deficits tend to preserve more lean mass and are easier to keep up until you reach your goal.
Why the 1,200 / 1,500 kcal floor warning matters
Widely cited nutrition guidance suggests adults generally should not eat below about 1,200 kcal/day (women) or 1,500 kcal/day (men) without medical supervision. Diets below that floor raise the risk of nutrient shortfalls, fatigue, and muscle loss, and are difficult to sustain safely without professional guidance. If your chosen stats and pace produce a target under that floor, this calculator shows a warning rather than a silent number — the usual fix is picking a smaller weekly pace or speaking with a doctor or registered dietitian.
Limits of this estimate
- It's a planning estimate, not a guarantee. Early weight loss often includes water weight, and the body's energy needs drift down somewhat as you lose weight (metabolic adaptation) — re-check your numbers every few weeks.
- Body composition isn't captured. Mifflin-St Jeor uses total body weight, so it can under- or overestimate for very muscular or very lean bodies.
- Activity level is self-reported. Most people overestimate how active they are; if progress stalls, try the tier below the one you picked rather than eating less.
- This is educational information only — not medical, nutrition, or fitness advice. Anyone with a health condition, an eating disorder history, or who is pregnant or breastfeeding should speak with a qualified professional before changing their diet.
Sources & further reading
- CDC Healthy Weight — guidance on safe weight-loss rates and energy balance
- Dietary Guidelines for Americans — calorie needs by age, sex, and activity level
- NHLBI (NIH) Aim for a Healthy Weight — BMI, calorie targets, and behavior guidance
- Academy of Nutrition and Dietetics — evidence-based nutrition and dietitian referrals
Frequently asked questions
How many calories should I eat to lose weight?
Start from your maintenance calories (TDEE), which this calculator estimates from your sex, age, height, weight and activity level using the Mifflin-St Jeor formula. Eating below that maintenance number creates the calorie deficit needed for weight loss. For example, a moderately active 35-year-old woman, 165 cm and 70 kg, has a TDEE of roughly 2,160 kcal; choosing a 0.5 kg/week pace subtracts about 550 kcal/day, for a daily target near 1,610 kcal. Pick a pace you can sustain — small, steady deficits are easier to stick to than extreme ones.
What is the 7,700 kcal per kilogram rule, and is it accurate?
One kilogram of body fat stores roughly 7,700 kcal (about 3,500 kcal per pound), so this calculator divides your weekly pace by 7 to get a daily deficit target. It's a useful planning estimate, not a physical law: early weight loss includes water weight, the body's energy needs drop somewhat as you get lighter (metabolic adaptation), and muscle versus fat loss varies by person. Treat the timeline as a rough guide and re-check your numbers every few weeks as your weight changes.
Why does the calculator warn me below 1,200 or 1,500 calories a day?
Widely cited guidance suggests adults generally should not eat below about 1,200 kcal/day (women) or 1,500 kcal/day (men) without medical supervision, since very low intakes raise the risk of nutrient deficiency, fatigue, and muscle loss. If your chosen pace pushes your target under that floor, this calculator shows a warning — the fix is usually to choose a smaller weekly pace (0.25 or 0.5 kg/week) or to talk to a doctor or registered dietitian before going lower.
What if my goal weight or pace doesn't make sense?
The calculator requires a goal weight below your current weight, since it is built around a calorie deficit for weight loss — if you want to maintain or gain weight, try a maintenance or TDEE calculator instead. Extreme height/weight combinations trigger a "double-check your numbers" note, and very aggressive paces (like 1 kg/week) at a small body size often hit the low-calorie floor warning above, since there isn't enough of a maintenance budget to cut that much safely.
Is my health information sent to a server?
No. This calorie deficit calculator runs entirely in your browser — your sex, age, height, weight and goal never leave your device, and nothing is uploaded or stored on a server. There's no sign-up and no tracking, so you can plan a weight-loss target privately.