What is a calorie deficit?
A calorie deficit means you consistently take in less energy than your body uses. Your body covers the gap from stored energy, and your weight trends down over time. That is the mechanism behind weight loss, whichever eating pattern you prefer.
| Example daily calculation | Calories |
|---|---|
| Estimated maintenance (TDEE) | 2,400 kcal |
| Food and drink intake | 1,900 kcal |
| Daily calorie deficit | 500 kcal |
Maintenance is also called total daily energy expenditure, or TDEE. You can sense-check it with our TDEE calculator, or read what a calorie deficit is and how it works.
A deficit is not a moral score. A larger one does not make you more disciplined, and a smaller one does not mean you are doing badly. The best target is the smallest deficit that produces a useful trend while leaving enough food for nutrition, energy and ordinary life.
How large should your calorie deficit be?
For many adults, a moderate starting deficit is easier to repeat than an aggressive cut. The NHS suggests reducing intake by around 600 calories a day, while the CDC describes gradual loss of about 0.45–0.9 kg (1–2 lb) a week as more likely to stay off than faster loss. These are general guides, not a requirement to lose at the fastest end.
| Daily deficit | Rough starting pace | Best fit | Main trade-off |
|---|---|---|---|
| 250 kcal | About 0.2 kg / 0.5 lb a week | A gentle start; flexibility first | Progress can hide in normal scale noise |
| 500 kcal | About 0.45 kg / 1 lb a week | A practical default for many adults | Requires portion awareness |
| 750 kcal | About 0.7 kg / 1.5 lb a week | Higher needs while staying above the floor | More hunger and fatigue |
| 1,000 kcal | About 0.9 kg / 2 lb a week | Not a routine default; discuss with a clinician | Harder to sustain and nourish well |
The pace uses the old energy conversion only as a short-term illustration. Real loss is not perfectly linear. If the chosen deficit pushes intake below the safety floor, the calculator reduces the deficit automatically.
What do your results mean?
| Result | What it means | How to use it |
|---|---|---|
| Current maintenance | Estimated calories used at your present weight | Treat it as a starting estimate |
| Starting calorie target | Maintenance minus your safe, effective deficit | Aim near it on average |
| Projected goal date | The date the daily model reaches your goal | Use it for planning, not as a deadline |
| Goal maintenance | Estimated calories that may maintain your goal weight | Recalculate from real-world data on arrival |
The result keeps your current activity setting throughout. For a fuller explanation, see how many calories to eat to lose weight.
Why does the goal-date projection slow down?
A lighter body generally uses less energy than a heavier one. If you keep eating the same starting target, the gap between intake and maintenance becomes smaller as you lose. The calculator holds starting intake fixed but recalculates Mifflin-St Jeor BMR, TDEE and fractional age every projected day.
The model uses 7,700 kcal/kg as a transparent approximation. This improves on extending a fixed 3,500 kcal/lb rule forever, but it is not the full NIDDK dynamic physiological model and cannot predict future hormones, spontaneous movement, adherence or body composition.
What is the safe calorie floor?
Without medical supervision, the calculator will not set intake below 1,200 kcal a day for the female equation or 1,500 kcal a day for the male equation. These are guardrails, not ideal targets and not proof that a low intake is right for you.
| Formula selection | Minimum intake | If the chosen deficit crosses it |
|---|---|---|
| Female equation | 1,200 kcal/day | Intake stays at 1,200; projected pace is reduced |
| Male equation | 1,500 kcal/day | Intake stays at 1,500; projected pace is reduced |
This adult tool is not intended for pregnancy, breastfeeding, eating-disorder recovery, medically supervised diets, or conditions and medication affecting weight, appetite, blood sugar or fluid balance. Ask a doctor or registered dietitian for a personal target in those situations.
How should you use your daily target?
Think weekly, not perfectly. Your calorie target is a centre point: eating a little above it one day and below it another can still produce the intended average. Do not compensate for a social meal by starving the next day; return to your usual plan at the next meal.
Build meals around filling, nourishing foods you enjoy. Protein-rich foods, fruit, vegetables, higher-fibre carbohydrates and measured sources of fat can make a deficit easier to live with, but no single food must be banned.
| Check-in | What to look at | Sensible response |
|---|---|---|
| First 2 weeks | Whether the target feels manageable | Learn the routine; ignore individual weigh-ins |
| After 3–4 consistent weeks | Average weight trend | Keep the target if trend and wellbeing are acceptable |
| Every 4–6 weeks or after 5 kg lost | Updated weight, activity and maintenance | Recalculate |
| Flat for 3–4 consistent weeks | Tracking gaps, portions, activity and water retention | Check inputs and habits before a large cut |
How accurate is a calorie deficit calculator?
It is a structured starting estimate. Mifflin-St Jeor was developed from measured resting energy expenditure, but no equation can see exact muscle mass, genetics, daily movement or food-tracking error. Activity multipliers add another estimate.
The most useful correction comes from your own trend. If weight changes broadly as expected over several consistent weeks, the target is close enough to act on. Persistent or unexplained weight change belongs in a conversation with a health professional, not an ever-lower target.
Frequently asked questions
What calorie deficit should I use to lose weight?
For many adults, the moderate option in the deficit table is a reasonable starting point. Choose the gentler option if hunger, a smaller body size or a busy routine makes consistency difficult. The calculator will reduce any selection that would cross its safety floor.
Does a 500-calorie daily deficit always mean one pound a week?
No. That is a useful short-term rule of thumb, not a guarantee. Your energy needs fall as weight drops, and scale weight also reflects water, digestion and other changes. The adaptive timeline recalculates estimated TDEE instead of extending the starting pace in a straight line.
How many calories should I eat to lose weight?
There is no honest universal number. Start with your estimated TDEE, subtract a manageable deficit, and respect the appropriate safety floor. Your age, height, weight, sex used by the equation and activity all affect the result.
Can I lose weight without counting calories?
Yes. A deficit still has to exist, but you can create it through repeatable portions, meal structure and food choices without logging every item. The calculator can give you a sense of scale even if you use the number only as a guide.
Should I eat back calories shown by my fitness tracker?
Usually not automatically. The activity multiplier already includes your typical movement, and wearable calorie estimates can be uncertain. If your training volume changes substantially, update the activity setting and use your weight trend and recovery to calibrate the result.
Why did my projected goal date move later?
Usually because your current weight, estimated activity, effective deficit or start date changed. The date also moves later when the safe floor prevents the full chosen deficit. That is the calculator protecting the guardrail, not you doing anything wrong.
Why will the calculator not go below its calorie floor?
Very low intakes can make adequate nutrition difficult and should be planned with clinical supervision. The floor is a safety boundary, so the tool lowers the effective deficit instead of producing a more dramatic date.
How often should I recalculate my calorie deficit?
Use the check-in table above while actively losing, and recalculate sooner if your weight, activity or routine changes meaningfully. A target based on an older, heavier body gradually becomes less effective.
Who should not use this calculator?
It is not designed for children, pregnancy, breastfeeding, eating-disorder recovery or medically supervised diets. If a health condition or medication affects your weight or appetite, use a target set with your doctor or registered dietitian.