The short answer
For most adults, a deficit of about 500 to 750 kcal a day is the range you'll see in clinical guidance. The 2013 adult obesity guideline from the American Heart Association, American College of Cardiology and The Obesity Society lists exactly those two numbers as one way to set a reduced-calorie diet.
CDC frames it by pace instead: gradual loss of about 1 to 2 pounds a week is more likely to stick than faster loss. Those two ideas line up roughly, because a 500 kcal daily gap is 3,500 kcal a week, the old shorthand for one pound.
Why one number doesn't fit everyone
A 500 kcal deficit means very different things for different people. If your TDEE is 3,000, it's about 16.7% of what you burn. If your TDEE is 1,800, it's about 28%, and your intake would drop to 1,300.
That's why many people think in percentages of TDEE. At a 2,400 kcal TDEE, 10% is 240 kcal, 20% is 480 and 25% is 600. A smaller body has less room to cut before intake gets low, so the same fixed number can be comfortable for one person and harsh for another.
- TDEE 3,000: a 500 kcal deficit is about 16.7%
- TDEE 2,400: a 500 kcal deficit is about 20.8%
- TDEE 2,000: a 500 kcal deficit is 25%
- TDEE 1,800: a 500 kcal deficit is about 28%
Bigger isn't faster for long
A large deficit looks great on paper. The 3,500-calorie rule says 1,000 kcal a day should mean 2 pounds a week forever. It doesn't work that way. NIH researcher Kevin Hall and colleagues showed that as you lose weight, your body burns less, so the same deficit shrinks on its own and loss slows.
Large deficits are also harder to live with. Hunger, low energy and worse workouts can make the plan hard to keep. A plan you can hold for months usually beats one you abandon after three weeks.
Signs your deficit is too big
Pay attention to how you feel, not just the scale. If any of these show up and stick around, ease off and talk to a doctor or registered dietitian.
- Constant hunger that makes it hard to think about anything else
- Dizziness, unusual tiredness or trouble sleeping
- Workouts falling apart or injuries piling up
- Changes to your menstrual cycle
- Tracking that's turning into anxiety or rigid rules about food
How to set yours
Start with a TDEE estimate, then pick a moderate deficit. Our calorie deficit calculator shows the gap per day and per week and lays out 5% to 25% options side by side. It won't go below 1,000 kcal a day, the same floor the NIDDK Body Weight Planner uses, but that's a tool limit, not a safe target.
Hold the plan for a few weeks and watch your average weight. If nothing has moved, check your TDEE and logging before cutting more. If you're losing faster than about 2 pounds a week after the first couple of weeks, consider eating a bit more.
When to get help first
Skip the do-it-yourself approach if you're pregnant or breastfeeding, under 18, have a history of disordered eating, or take medication or have a condition that affects weight or appetite. Very low-calorie diets should only happen under medical supervision. A clinician can help you set a target that fits your health, not just your math.
Frequently asked questions
Is a 1,000 calorie deficit too much?
For many people, yes. It's double the low end of the 500 to 750 kcal guideline range, and for a smaller person it can push intake very low. Talk to a clinician before going that far.
Can a deficit be too small?
A small deficit is safe but slow, and it's easily erased by estimation error in your TDEE or food log. If nothing changes after several weeks, a modest increase may help.
Should the deficit change as I lose weight?
Your TDEE drops as you get lighter, so the same intake gives a smaller deficit over time. Recalculate after meaningful weight change.
Is it better to eat less or exercise more?
Either creates a deficit. Most plans combine both, and CDC notes physical activity helps with keeping weight off once it's lost.
References
These sources support the method or guidance used for Calorie Deficit Calculator. Verify time-sensitive rules at the source.
Try the calculator
Open Calorie Deficit Calculator, enter your scenario, and compare its supporting rows with this guide's method and checks.