Your calorie number, shown in full.

Ask your fitness app where your calorie number comes from and you will usually get silence, a proprietary algorithm, or a cartoon. Here is the actual math, in full, the same published equation dietitians have used for decades. Bring a calculator and check ours.

Step 1: your BMR, from the Mifflin-St Jeor equation

Your basal metabolic rate is roughly what your body burns at complete rest. The Mifflin-St Jeor equation, published in 1990 and repeatedly validated since, estimates it for women as:

A worked example. A 34-year-old woman, 5’4” (162.5 cm), 150 pounds (68 kg):

• 10 × 68 = 680
• 6.25 × 162.5 = 1,016
• minus 5 × 34 = minus 170
• minus 161

BMR ≈ 1,365 calories. That is rest. Nobody lives at rest, so:

Step 2: multiply by your real activity

• Mostly sitting: × 1.2
• Lightly active, some walking and chores: × 1.375
• Active, on your feet or regular exercise: × 1.55
• Very active: × 1.725

Our example, lightly active: 1,365 × 1.375 ≈ 1,875 calories to maintain her current weight. This is called TDEE, total daily energy expenditure.

Step 3: adjust for your goal, with a floor

To lose fat, a sensible deficit is roughly 300 to 500 calories under maintenance, not more. To build, a small surplus or simply eating at maintenance with enough protein does the job. Two honesty rules matter here:

• A safety floor. Below roughly 1,200 calories, meeting your nutrient needs gets very hard, and the plan becomes miserable and unsustainable. We will not calculate you a number under our floor, ever, whatever a smaller number might promise.
• Close is good enough. Every formula is an estimate with a margin of error. Pick the number, live with it for three or four weeks, watch what happens, and adjust by 100 to 150 calories. That feedback loop beats any equation's precision.

Protein, while you are here

Sports-nutrition guidance from the ISSN lands, for most women who train, around 0.7 to 1 gram per pound of goal body weight daily. Protein protects muscle in a deficit and builds it in a surplus, and it is the single most skipped number in DIY plans. Our example might target around 120 grams a day.

Or let the quiz do the arithmetic

The free quiz runs exactly this calculation from your age, height, weight, and activity, applies your goal and the safety floor, sets your protein, and matches you to a program. You can check every number it gives you against this page. That is the point.

Keep reading: How much protein women need to build muscle · Strength training on a GLP-1 · 20-minute home workouts · What we refuse to sell you