A calorie deficit happens when you eat fewer calories than your body burns. To calculate it, find your maintenance calories (TDEE) with the Mifflin-St Jeor formula times an activity multiplier, then subtract 250 to 1,000 calories per day. A 500-calorie daily deficit leads to about 1 pound of fat loss per week. Use our free calorie deficit calculator to get your personal numbers in seconds.
What Is a Calorie Deficit?
A calorie deficit is simply the gap between the energy you take in and the energy you spend. Your body needs energy for everything: breathing, thinking, digesting food, and moving around. When food does not cover that need, your body pulls stored energy from fat tissue, and you lose weight.
One pound of body fat stores roughly 3,500 calories. This is the number that makes the whole method work. Create a total deficit of 3,500 calories and you lose about one pound. Spread that deficit across a week and you get the most common target: 500 fewer calories per day equals about 1 pound per week.
Why Do You Need to Know Your TDEE First?
You cannot calculate a deficit without a starting point. That starting point is your TDEE, or total daily energy expenditure. TDEE is the number of calories that keeps your current weight stable. It has two parts: your basal metabolic rate (BMR), which is what you burn at rest, and your activity calories, which is what you burn through daily movement and exercise.
Many people skip this step and guess. Guessing is the top reason diets fail, because a target of 1,500 calories means very different things to a 110-pound office worker and a 220-pound construction worker. Calculate your TDEE first and the rest is simple subtraction.
How Do You Calculate Your BMR?
The Mifflin-St Jeor equation is the most widely trusted BMR formula. It needs only your weight, height, age, and sex:
- Men: BMR = 10 x weight (kg) + 6.25 x height (cm) – 5 x age + 5
- Women: BMR = 10 x weight (kg) + 6.25 x height (cm) – 5 x age – 161
Let us work a full example. Take a 40-year-old man who weighs 90 kg (about 198 lb) and is 185 cm tall (about 6 ft 1 in):
- 10 x 90 = 900
- 6.25 x 185 = 1,156.25
- 5 x 40 = 200
- BMR = 900 + 1,156.25 – 200 + 5 = 1,861.25, or about 1,861 calories per day
Now a second example. A 28-year-old woman weighing 65 kg (about 143 lb) at 170 cm (about 5 ft 7 in):
- 10 x 65 = 650
- 6.25 x 170 = 1,062.5
- 5 x 28 = 140
- BMR = 650 + 1,062.5 – 140 – 161 = 1,411.5, or about 1,412 calories per day
How Do You Turn BMR Into TDEE?
Multiply BMR by an activity factor that matches your real daily life:
- 1.2 – Sedentary: desk job, little or no exercise
- 1.375 – Lightly active: light exercise 1 to 3 days per week
- 1.55 – Moderately active: moderate exercise 3 to 5 days per week
- 1.725 – Very active: hard exercise 6 to 7 days per week
- 1.9 – Extra active: very hard exercise or a physical job
Continuing our examples: the man is sedentary, so his TDEE = 1,861.25 x 1.2 = 2,233.5, or about 2,234 calories per day. The woman is moderately active, so her TDEE = 1,411.5 x 1.55 = 2,187.8, or about 2,188 calories per day. Notice that these are maintenance numbers: eating exactly these amounts would keep their weight steady.
How Do You Choose the Size of Your Deficit?
The 3,500-calorie rule gives you a simple menu:
| Daily Deficit | Weekly Deficit | Expected Loss per Week |
|---|---|---|
| 250 calories | 1,750 calories | 0.5 lb |
| 500 calories | 3,500 calories | 1 lb |
| 750 calories | 5,250 calories | 1.5 lb |
| 1,000 calories | 7,000 calories | 2 lb |
For most people, a 250 to 500 calorie daily deficit is the sweet spot: fast enough to stay motivated, gentle enough to keep energy, sleep, and training quality intact. Deficits of 750 to 1,000 calories suit people with more weight to lose, but they need more planning around protein and nutrients.
How Do You Get Your Final Calorie Target?
Subtract your chosen daily deficit from your TDEE. For the man in our example with a 1-pound-per-week goal: 2,234 – 500 = 1,734 calories per day. For the woman with a 1.5-pound-per-week goal: 2,188 – 750 = 1,438 calories per day.
One safety check before you lock in the number: most guidelines suggest staying at or above 1,200 calories per day for women and 1,500 for men unless a professional is supervising you. Both of our examples clear that floor comfortably.
Common Mistakes When Calculating a Deficit
- Picking too high an activity level. Be honest. If in doubt, choose one level lower and adjust after two weeks.
- Counting exercise calories twice. Your activity multiplier already includes exercise, so do not add burned calories on top unless you track them carefully.
- Expecting a perfectly straight line. Water retention, glycogen, and digestion make the scale bounce day to day. Judge progress by the two-week trend, not by single weigh-ins.
- Never recalculating. As you lose weight, your TDEE drops. Recalculate every 10 to 15 pounds lost and shrink your target to match.
Frequently Asked Questions
How do I calculate a calorie deficit by hand?
Calculate BMR with Mifflin-St Jeor, multiply by your activity factor to get TDEE, then subtract your desired daily deficit (for example, 500 calories for 1 pound per week). The result is your daily calorie target for weight loss.
What is the easiest formula for a calorie deficit?
The simplest version is: daily target = TDEE – 500. The 500-calorie deficit is the standard starting point because it produces about 1 pound of fat loss per week without severe hunger for most adults.
How do I calculate my deficit without a scale?
You can estimate with a tape measure or recent clothing sizes, but weight is much more reliable. A basic bathroom scale and a kitchen food scale are the two tools that make deficit math actually work in practice.
Can I calculate a deficit in pounds and inches?
Yes. Convert first: divide pounds by 2.20462 to get kilograms, and multiply total inches by 2.54 to get centimeters. For example, 180 lb equals 81.65 kg, and 5 ft 10 in (70 inches) equals 177.8 cm. Then use the same formulas.
How often should I recalculate my calorie deficit?
Recalculate every 10 to 15 pounds of weight lost, or every 6 to 8 weeks. A smaller body burns fewer calories, so keeping your old target will slowly erase your deficit and stall progress.
Does the deficit formula work for everyone?
It works as a starting estimate for most healthy adults. Athletes with high muscle mass, people with certain medical conditions, and teenagers should work with a professional, since standard formulas assume average body composition.
