How to Calculate a Calorie Deficit
To find your calorie deficit, estimate your maintenance calories, subtract the deficit you choose — usually 500 a day for about 1 lb a week at first — and check the result isn't below 1,200 calories a day for women or 1,500 for men. Recalculate as your weight drops.
A calorie deficit is just maintenance minus what you eat, but getting each piece right matters. Here are the five steps, worked end to end for a 35-year-old woman, 5 ft 4 in (162.6 cm), 165 lb (74.8 kg), low active. It's the core of any calorie deficit diet.
Step 1: Estimate your maintenance calories
Maintenance is your total daily burn. We estimate it with the 2023 National Academies equations rather than a resting-rate formula scaled by a guess. The low-active equation for a woman is:
TDEE = 575.77 − 7.01 × age + 6.60 × height(cm) + 12.14 × weight(kg)
For her that works out, by hand, to 575.77 − 245.35 (7.01 × 35) + 1,072.90 (6.60 × 162.56) + 908.59 (12.14 × 74.84) = about 2,312 calories a day. Most women like her fall between 2,066 and 2,558 — the equations' published standard error, which covers about two in three people.
There are separate equations for men and for each of the four activity levels, so the numbers shift with your details — the methodology has the full set. To skip the arithmetic, the TDEE calculator returns your maintenance and range directly.
Step 2: Choose your deficit
Cutting 500 to 1,000 calories a day below maintenance gives about 1 to 2 lb a week at first — a rate experts consider safe (Harvard Health Publishing). Pick a size you can actually hold; a smaller, steady deficit usually beats an aggressive one you abandon. Her daily targets:
| Daily deficit | Eat about |
|---|---|
| 250 | 2,062 |
| 500 | 1,812 |
| 750 | 1,562 |
| 1,000 | 1,312 |
Or let the calorie deficit calculator set the target and timeline for you.
Step 3: Check the floor
Don't take intake below 1,200 calories a day for women or 1,500 for men without a health professional's supervision (Harvard Health Publishing). All four of her targets clear 1,200 — but the 1,000-calorie option leaves only 112 to spare. Smaller or less active people reach the floor sooner, which is why a big deficit isn't automatically better.
Step 4: Set realistic expectations
A fixed deficit does not give fixed weekly loss. At 500 a day, here is where the NIH weight-change model (Hall et al. 2011) puts her against the old 3,500-calorie rule:
| Week | NIH model | 3,500 rule |
|---|---|---|
| 4 | 160.7 lb (72.9 kg) | 161.0 lb (73.0 kg) |
| 12 | 155.2 lb (70.4 kg) | 153.0 lb (69.4 kg) |
| 26 | 147.1 lb (66.7 kg) | 139.0 lb (63.0 kg) |
| 52 | 136.0 lb (61.7 kg) | 113.0 lb (51.3 kg) |
The model has her losing about 29.0 lb in a year — not the 52 lb the rule predicts — because her burn falls as she gets lighter. That gap is the whole reason to plan from the model, not the rule; see how many calories are really in a pound, or what a 500-calorie deficit really does week by week.
Step 5: Recalculate as you lose
Because a lighter body burns less, your maintenance — and so your target — drifts down as you go. At the same activity level, hers falls to about 2,257 after 10 lb lost and about 2,202 after 20 lb, roughly 55 calories a day per 10 lb. A 500-calorie deficit therefore means eating about 1,757, then about 1,702. Re-run the numbers every time the scale has moved noticeably.
Why we don't multiply BMR by an activity factor
Most calculators estimate resting burn and multiply it by an activity factor between 1.2 and 1.9. That multiplier table is a textbook convention we couldn't trace to a primary source, and small changes in it move the answer a lot. The 2023 equations instead predict the whole day directly from doubly labeled water data, with activity already built in — more on that in the methodology.
When your results don't match the scale
Every estimate carries a range, so treat your number as a starting point. Weigh in regularly and compare your trend with the model's line rather than any single morning. If you're consistently slower over several weeks, the likeliest reasons are that your real maintenance is lower than the estimate, or that intake has crept up — the NIH model's authors note that real-world programs usually drift from their target over time (Hall et al. 2011). Lower your target a little and re-check, never below the floor. Our guide to being in a deficit but not losing weight walks through the rest.
Frequently asked questions
How do I figure out my calorie deficit?
Maintenance minus the deficit you pick. In the worked example, 2,312 minus 500 = about 1,812 calories a day.
How do I calculate my calorie deficit to lose weight?
Estimate maintenance from the 2023 equations; pick a deficit of 500 to 1,000 a day; check it isn't below 1,200 (women) or 1,500 (men); expect about 1 to 2 lb a week at first; recalculate as you lose.
Should I add exercise calories back?
If the activity level you chose already includes your workouts, adding them again counts them twice.
How often should I recalculate?
Whenever your weight has changed noticeably. For the worked example, maintenance drops about 55 a day per 10 lb lost.
Is a 1,000-calorie deficit OK?
It's the top of the 500 to 1,000 range Harvard Health describes; check the floor first, because a 1,000-calorie cut pushes smaller or less active people below the minimum. See whether a 1,000-calorie deficit is safe.
Sources
- National Academies (2023), Dietary Reference Intakes for Energy, Table S-1
- National Academies (2023), chapter 7, activity levels
- Hall KD et al., The Lancet 2011 (NIH author manuscript)
- Harvard Health Publishing, Calorie counting made easy
- CDC, Adult BMI categories