Losing fat comes down to eating a bit less than you burn, long enough to see it. The hard part isn't the math. It's picking a number you can live with and adjusting it when your body doesn't follow the formula. Here's the process I use.
Step 1: Find your maintenance
Your maintenance calories are what you'd eat to stay the same weight. A formula like Mifflin-St Jeor estimates it from your age, height, weight, sex and how active you are. Get yours in a minute with the free calorie calculator.
Treat it as a starting guess. Formulas can be off by a few hundred calories either way.
Step 2: Pick a deficit
Most people do well eating 300 to 500 calories below maintenance. That usually means losing about 0.5 to 1% of your bodyweight a week, around 1 to 2 lb for a 180 lb person.
- Slower (about 300 under) keeps more muscle and energy. Good if you're already fairly lean.
- Faster (500 or more under) gets results quicker but makes training and hunger harder. Better if you have more to lose.
Going much lower than that rarely speeds things up for long. It mostly makes you hungrier and more tired until you stop.
Step 3: Set your protein
Keep protein high while you diet, around 0.8 to 1 gram per pound of bodyweight, so the weight you lose is fat, not muscle. More on protein here. The macro calculator splits your calories into protein, carbs and fat for you.
Step 4: Keep lifting
Lifting is the signal that tells your body to keep its muscle. Don't switch to only cardio while you diet. Keep your main lifts heavy, even if you can't add weight as fast as before.
Step 5: Adjust from real results
Weigh yourself a few mornings a week and watch the weekly average, not single days. Water, salt and carbs move the scale day to day.
- Losing about what you planned? Change nothing.
- Nothing moved after 2 to 3 weeks? Eat 100 to 200 fewer calories a day, mostly from carbs and fat.
- Losing much faster than planned and training feels bad? Eat 100 to 200 more.
That's the whole game: start with a good estimate, then let your own numbers correct it.