For most adults, losing weight means eating 300 to 500 calories a day below what you burn, which usually lands somewhere between 1,400 and 2,200 a day. That is the honest short answer. The exact number depends on your size, age, sex and how much you move, so the rest of this post is about finding yours: what your body burns, how much to take off, where the floor is, and what to do when the scale ignores the math.
If you just want the number, the calorie deficit calculator does the arithmetic below for you and shows the answer as a range. Read on if you want to know why it says what it says.
Start with what you burn, not what you eat
Every “how many calories” answer is really two questions. How much does your body burn in a normal day, and how far below that do you want to eat. The first number is called your TDEE, total daily energy expenditure. It is your resting metabolism plus everything you do on top: walking, working, training, digesting food.
The formula almost every calculator uses is Mifflin-St Jeor. It takes your weight, height, age and sex and gives a resting figure, then multiplies by an activity factor. Here is what it looks like for a 35-year-old woman, 165 cm, 75 kg, with a desk job and some walking:
| Step | Number |
|---|---|
| Resting metabolism (lying still all day) | about 1,450 kcal |
| Times a light-activity factor (desk job, some walking) | about 2,000 kcal |
| The honest range, plus or minus 10% | 1,800 to 2,200 kcal |
That last row matters. The formula is a population average, and real people sit anywhere in a band around it. Two women with identical stats can burn a few hundred calories apart because of muscle, fidgeting, job, and how carefully they log. A calculator that hands you one exact number is rounding off the part you actually need to know. (The TDEE calculator explains the range in more detail.)
Subtract a deficit you can hold for months
A kilogram of body fat stores roughly 7,700 calories. So the pace you pick sets the daily deficit:
| Pace | Weekly loss | Daily deficit | Who it suits |
|---|---|---|---|
| Gentle | 0.25 kg (½ lb) | about 275 kcal | Close to goal, or anyone who has quit diets from hunger before |
| Moderate | 0.5 kg (1 lb) | about 550 kcal | The default for most people |
| Fast | 0.75 kg (1½ lb) | about 825 kcal | Larger bodies with room to cut, short term |
| Aggressive | 1 kg (2 lb) | about 1,100 kcal | Rarely worth it; hunger, fatigue and muscle loss catch up fast |
For the woman in the example, moderate pace means about 2,000 minus 550, so roughly 1,450 calories a day, with the honest range being 1,250 to 1,650 once you carry the maintenance uncertainty through. Gentle pace puts her at about 1,725.
The thing nobody tells you is that the smaller deficit usually wins. Not because it burns more fat per day, it does not, but because you are still doing it in month three. A 550-a-day deficit you abandon after two weeks loses less weight than a 275-a-day deficit you keep for a year. Pick the pace by asking “can I eat like this for three months,” not “how fast can this go.”
1,200 is a floor, not a target
Somewhere along the way 1,200 calories became the internet’s default diet number. It is not a target. It is roughly the point below which most women cannot get enough protein and nutrients from real food, and hunger takes over. For men that line is around 1,500.
If a calculator hands you a number under those, the fix is not to eat 1,200 and push through. The fix is a slower pace. A target you can hold beats one you white-knuckle for a fortnight and then overeat your way out of. The deficit calculator flags this and refuses to headline a number below the floor, which is deliberately annoying.
What actually goes wrong
The math above is simple. The reason it fails for people is almost never the math.
The estimate was high for you. The formula was fit on averages. If your true maintenance is at the low end of the range, a 500 deficit on paper is a 300 deficit in practice, and the scale moves at half the speed you expected. Nothing is broken. You just need the second half of the process, below.
Logging is missing calories. Cooking oil, salad dressing, the spoon of peanut butter, the end of the kids’ dinner, the “just a taste.” These add up to a few hundred calories a day for most people and never make it into the log. If you have been in a deficit for a month and the scale has not moved, this is the first thing to check, and the honest fix is weighing food for one week, not cutting the target again.
Water is hiding fat loss. Salt, stress, poor sleep, a hard workout, and where you are in your cycle all move daily weight by more than a day’s fat loss ever could. You can lose fat for two weeks and see the scale go up. Judge the deficit on the two-week trend, not on any single morning.
The deficit was too big. Hunger climbs, training feels worse, you get cold, and one day the plan quietly ends. That is not a willpower problem, it is a pace problem. Shrink the deficit by 100 to 200 a day and keep going.
The two-week rule
This is the part that does the work. The calculator gives you a starting guess. Your own weight trend tells you whether it was right.
- Pick the middle of your range and eat there for 14 days, logging honestly. Do not change anything mid-way, however the scale wobbles.
- Compare the trend to the plan. Weight moving at roughly the pace you chose? Change nothing. Boring is winning.
- If it is flat after two honest weeks, trim 100 to 150 calories a day, or add a bit of daily walking. Not both at once, or you will not know which one worked.
- If it is dropping faster than planned and you are hungry, add 100 to 200 back. The estimate was low for you.
Repeat every couple of weeks. Within a month or two you will know your real maintenance better than any formula can guess it, because you measured it.
What about exercise calories?
If the activity level you picked already includes your training, they are counted. Do not add them again. Watches and machines overstate exercise burn, often by a third or more, and “eating back” those calories is one of the most common ways a deficit turns into maintenance without anyone noticing. Only add calories for activity that is genuinely beyond what you selected, and be conservative when you do.
Where the app fits
None of this needs an app. A notebook works. What an app does is make the two-week rule cheap enough that you actually do it: log a meal in a few seconds, see the weekly average rather than today’s number, and compare it against your weight trend without doing the spreadsheet yourself.
That is what PocketChomp is built for. Logging, barcode scanning, the full Canadian food database and every nutrient are free and stay free. It runs without an account, keeps your log on your phone, and does not show ads. If you want it to work out your real maintenance from your own data instead of a formula, that is the paid part, and you can decide about that once the free version has earned it.
Start with the calorie deficit calculator, take the middle of the range, and give it two weeks.