The one rule: eat less than you burn
Weight loss comes down to a calorie deficit — taking in less energy than your body uses, so it makes up the difference by burning stored fat. Every diet that works, whatever it's called, works because it puts you in a deficit. You don't need a special plan; you need a target and a way to stick to it.
Getting to your target is two steps: estimate your maintenance calories, then decide how big a deficit to run.
Step 1 — Find your maintenance calories
Your maintenance number is your TDEE — Total Daily Energy Expenditure — the calories you burn in a full day including movement and exercise. Estimate your BMR with the Mifflin-St Jeor equation, then multiply by an activity factor.
Men: BMR = (10 × weight kg) + (6.25 × height cm) − (5 × age) + 5 Mifflin-St Jeor — then TDEE = BMR × 1.2 (sedentary) to 1.9 (very active)
Most people fall between × 1.375 (light exercise 1–3 days a week) and × 1.55 (moderate exercise 3–5 days a week). Be honest — a busy day at a desk is still sedentary. Our full guide to calculating your TDEE breaks the multipliers down, or the TDEE calculator does it for you.
Step 2 — Choose your calorie deficit
Subtract from maintenance. The size of the cut sets your speed — and your risk of losing muscle or burning out.
| Deficit | Rough weekly loss | Best for |
|---|---|---|
| 10–15% below TDEE | 0.5 lb | The last few pounds; protecting muscle; minimal hunger |
| 20% below TDEE (~500/day) | 1 lb | The default — steady, sustainable, works for most people |
| 25–30% below TDEE | 1.5–2 lb | Higher starting body fat, short-term, under guidance |
A safe general rule is to lose 0.5–1% of your body weight per week. Faster than that and a growing share of the loss is muscle and water rather than fat.
Why the "3,500 calories = 1 pound" rule overpromises
The classic rule says a pound of fat holds about 3,500 calories, so a 500-a-day deficit should drop 1 lb a week forever. In practice it slows down. As you get lighter you burn fewer calories, and your body adapts by trimming non-exercise movement and becoming slightly more efficient. Expect the first weeks to track the math, then the rate to taper. That's normal — it's a signal to recalculate, not to slash calories further.
The floors — don't eat below these
- Women: not below 1,200 calories a day. Below this it's hard to hit your vitamin, mineral, and protein needs.
- Men: not below 1,500 calories a day. Same reason — the diet becomes nutritionally thin.
- Cap the rate at ~1% of body weight per week. Quicker loss costs muscle and tanks energy, training, and mood.
- Very low-calorie diets (under 800) are a medical tool. They exist, but only under supervision — not a DIY choice.
If your maintenance is low enough that a full 500-calorie deficit would push you under the floor, take a smaller deficit and add activity instead. A daily walk widens the gap without cutting food.
A worked example
A 35-year-old woman, 5 ft 5 in, 170 lb, lightly active (gym twice a week, mostly desk work).
- BMR: (10 × 77) + (6.25 × 165) − (5 × 35) − 161 = 770 + 1,031 − 175 − 161 = 1,465
- TDEE: 1,465 × 1.375 = ≈ 2,015 calories (maintenance)
- Target: 2,015 − 500 = ≈ 1,515 calories a day
That's above the 1,200 floor, predicts roughly 1 lb a week to start, and leaves room to eat enough protein. She'd hold it for 3–4 weeks, then recheck against the scale.
Protein matters more in a deficit
When you eat below maintenance, your body will take some energy from muscle unless you give it reasons not to. Two things protect lean mass: enough protein and some resistance training. Aim for 0.7–1 g of protein per pound of body weight per day. Protein also has the highest satiety of the three macros, so it makes the deficit easier to hold.
When the scale stalls
Weight doesn't fall in a straight line. Water retention from a hard workout, a salty meal, or hormonal shifts can mask two weeks of real fat loss. Before changing anything, give it two to three weeks and watch the trend, not the daily number. If the trend is genuinely flat and you've been consistent, drop your target by 100–150 calories or add 15–20 minutes of daily walking, then reassess.
Frequently asked questions
Is 1,200 calories a day enough to lose weight?
For many smaller or less active women, a target near 1,200 will produce a deficit and steady loss. But 1,200 is a floor, not a goal — if your maintenance is 2,000, you don't need to drop to 1,200 to lose weight, and eating that low makes the diet harder to stick to and harder to get enough protein.
How many calories to lose 2 pounds a week?
Roughly a 1,000-calorie daily deficit. That's aggressive — only appropriate if your maintenance is high and your starting body fat is high, and it's hard to sustain. Most people do better losing 1 lb a week on a 500 deficit.
Do I need to count calories, or can I just eat less?
Eating less works if it puts you in a deficit — but people routinely underestimate portions by 20–30%. Counting for a few weeks calibrates your judgement, then many people can maintain the deficit by eye. Tracking is a learning tool, not a life sentence.
Should I eat back the calories I burn exercising?
If your maintenance number already included an activity multiplier, no — that exercise is baked in, and eating it back double-counts it. Only add calories back if you calculated maintenance as sedentary and log workouts separately.
Why am I not losing weight in a calorie deficit?
Usually one of three things: the deficit is smaller than you think (untracked extras), water retention is masking fat loss on a short timescale, or your maintenance estimate was too high. Track tightly for two weeks, weigh under consistent conditions, and recalculate your TDEE at your current weight.