To lose weight, you need to eat fewer calories than your body burns. That part is simple. The harder questions are how many fewer, and how to pick a number you can live with for more than a week. This guide gives you a clear answer, and clears up a popular rule that has misled people for years.
Start with your maintenance calories
Before you can create a deficit, you need to know what you’re subtracting from. That figure is your maintenance level, often called your TDEE (Total Daily Energy Expenditure). It’s the number of calories your body burns in a day once you add up everything: staying alive, moving around, and exercising.
Your TDEE depends on your sex, age, height, weight and how active you are, so there’s no single number that works for everyone. The most reliable way to estimate it is the Mifflin-St Jeor equation, which is what our TDEE calculator uses. Work out your figure first, then come back here. Everything else builds on it.
What a calorie deficit actually is
A calorie deficit simply means eating less energy than you burn. When that happens, your body makes up the difference from stored energy, mostly body fat. There is no way around this: no food, meal timing or diet trick causes fat loss without a deficit somewhere underneath it.
The size of your deficit decides how fast you lose. A bigger gap means faster loss, but also more hunger and a higher chance of giving up or losing muscle along the way. That trade-off is the whole game.
The 3,500-calorie rule, and why it’s misleading
You’ve probably heard that cutting 500 calories a day loses you a pound a week, because a pound of fat holds about 3,500 calories. It’s a tidy bit of maths, and it’s the basis of most weight-loss advice online.
It’s also not how the body works.
The rule assumes you burn pure fat and nothing else, at a fixed rate, forever. In reality, when you lose weight you lose some lean tissue alongside fat, and your metabolism gradually drops as you get lighter, because a smaller body burns fewer calories. So the same deficit produces less and less loss over time. The 3,500-calorie rule tends to overpromise, which is exactly why so many people feel like they’re “doing everything right” and stalling.
The takeaway isn’t to give up on deficits. It’s to expect a realistic, slowing curve rather than a straight line, and to treat any calculator result as a starting point you adjust from, not a guarantee.
How big should your deficit be?
For most people, a deficit of 300 to 500 calories a day hits the sweet spot. It produces noticeable progress, around 0.3 to 0.7% of your body weight per week, while staying gentle enough to sustain and to protect muscle.
Here’s a rough guide based on how aggressive you want to be:
| Pace | Daily deficit | Roughly per week |
|---|---|---|
| Gentle | 250 kcal | 0.25 kg |
| Steady | 500 kcal | 0.5 kg |
| Faster | 750 kcal | 0.75 kg |
| Aggressive | 1,000 kcal | 1 kg |
Our calorie deficit calculator does this maths for you: enter your maintenance calories, pick a pace, and it shows the daily target to eat.
A few sensible limits. Losing more than about 1 kg (2 lb) a week usually isn’t fat alone, and large deficits get harder to sustain fast. Dropping below roughly 1,200 calories a day makes it tough to get enough nutrients and is best done only with professional guidance.
Why slower is usually smarter
It feels counterintuitive, but a smaller deficit often wins. Here’s why:
- You keep more muscle. Muscle is what gives you shape and keeps your metabolism higher. Aggressive deficits burn through it.
- You’re more likely to stick with it. A plan you can follow for months beats a punishing one you quit in two weeks.
- You feel better. Crushing hunger, low energy and poor sleep all come with very large deficits, and all make you more likely to give up.
The best diet is the one you can actually keep doing. A modest deficit you barely notice will out-perform an extreme one you abandon.
Rule of thumb: if your weight-loss plan feels miserable, it's probably too aggressive. Ease the deficit. A slower pace you stick to beats a fast one you quit.
Make your deficit easier with protein
One simple change makes a deficit far more comfortable: eat enough protein. It’s the most filling of the three macronutrients, so it blunts hunger, and it helps preserve muscle while you lose fat, which keeps your metabolism higher.
A higher-protein diet is one of the most reliable ways to make fat loss feel sustainable rather than miserable. Our protein calculator gives you a daily target based on your weight and goal.
Putting it together
- Find your maintenance calories with the TDEE calculator.
- Subtract a sensible deficit, 300 to 500 calories for most people, using the calorie deficit calculator.
- Get enough protein to stay full and hold on to muscle.
- Track for a few weeks, then adjust. If the scale hasn’t moved after three to four weeks of consistency, trim another 100 to 200 calories or add a little more daily movement.
Weight loss isn’t about finding one perfect number. It’s about picking a reasonable target, giving it time, and adjusting based on what your body actually does.