There is no single number that works for everyone, but there is a simple, reliable way to find yours: estimate how much you burn, eat a little less than that, watch the scale for a few weeks, and adjust. This article walks through each step with the numbers.
Step 1: estimate what you burn
Your total daily energy expenditure (TDEE) is the calories you burn in a day, including exercise and ordinary movement. The most common way to estimate it is the Mifflin-St Jeor equation for resting metabolism, multiplied by an activity factor:
- Men: 10 × weight (kg) + 6.25 × height (cm) − 5 × age + 5
- Women: 10 × weight (kg) + 6.25 × height (cm) − 5 × age − 161
Then multiply by activity: about 1.2 if you mostly sit, 1.375 for light exercise a few days a week, 1.55 for moderate exercise most days, 1.725 if you train hard most days.
For example, a 35-year-old woman, 165 cm and 75 kg, who trains three days a week: 10 × 75 + 6.25 × 165 − 5 × 35 − 161 = 1,445 kcal at rest, × 1.375 ≈ 1,990 kcal a day.
This is an estimate with an error of a few hundred calories either way. That is fine, because step 4 corrects it.
Step 2: choose a deficit
Losing weight means eating less than you burn. A deficit of about 500 calories a day is the standard starting point. For the example above that's roughly 1,500 kcal a day.
Two guardrails:
- Don't go below about 1,200 kcal (women) or 1,500 kcal (men) without medical supervision. It's hard to get enough protein and micronutrients below that, and adherence collapses.
- A smaller deficit is fine if you have less to lose. Someone with 5 kg to lose does better at a 300 kcal deficit than a 700 kcal one.
Step 3: pick a rate, not just a number
A sensible rate of fat loss is 0.5–1% of body weight per week. For a 75 kg person that's roughly 0.4–0.75 kg (about 1–1.5 lb) a week. Faster than that and you tend to lose more muscle, feel worse, and quit sooner. Slower is perfectly fine if it's sustainable.
Keeping protein high and lifting weights during a deficit are the two things that protect muscle while you lose fat. Our guides on how much protein to eat per day and progressive overload cover both.
Step 4: adjust to the trend
This is the step that makes the first three forgiving. After two or three weeks of logging and weighing in:
- Losing within the target range? Keep going. Nothing to change.
- Losing faster than 1% a week? Add 100–200 calories, mostly protein and carbs.
- Not losing, or losing much slower than expected? First check the logging. Unlogged snacks, drinks, oils and weekend meals explain most stalls. If the log is honest, take 100–200 calories off and give it another two weeks.
Weigh yourself at the same time of day, ideally most mornings, and compare weekly averages rather than individual days. Daily weight swings by 1–2 kg from water and food alone; the average is what tells the truth.
If you text Bay your weigh-ins, it runs this review for you once a week: it compares your logged intake to the trend on the scale and nudges the target rather than asking you to try harder. It's the same loop described here, done automatically.
Questions, answered.
Tap a question.
Should I eat back exercise calories?
Mostly no. Watches and machines overestimate burn, and the activity factor in step 1 already accounts for your training. Eat to the target and let the scale trend guide adjustments.
Do I need to count exactly?
No. A consistent estimate is more useful than an occasionally precise one. Logging by text or photo is accurate enough when it's done every day.
What about rest days vs training days?
Eating a little more on training days and less on rest days is fine and can help performance, but it's an optimisation, not a requirement. Nail the weekly average first.
Related reading
Bay is a software assistant, not a doctor, dietitian or certified trainer. Nothing here is medical, nutrition or professional advice; check with a professional before changing your diet or training.