How many calories should you eat per day?
Daily calorie needs depend on body size, age, sex and activity. A calculator can provide a starting estimate, but real requirements change with routines and health circumstances.
Start with the idea
A common approach first estimates basal metabolic rate, the energy used at rest, and then applies an activity factor to estimate total daily energy expenditure.
Fynzo uses the Mifflin–St Jeor equations. For men: 10W + 6.25H − 5A + 5. For women: 10W + 6.25H − 5A − 161, where W is kilograms, H is centimetres and A is age in years.
Worked example
For a 30-year-old man weighing 80 kg at 180 cm, estimated BMR is 10×80 + 6.25×180 − 5×30 + 5 = 1,780 kcal/day.
If an activity factor of 1.375 is selected, maintenance is approximately 2,448 kcal/day. This is an estimate to observe and adjust, not a prescription.
Quick reference
| Item | Meaning |
|---|---|
| Sedentary | BMR × about 1.2 |
| Light activity | BMR × about 1.375 |
| Moderate activity | BMR × about 1.55 |
| Very active | BMR × about 1.725 |
Common mistakes
- Selecting an activity level that is higher than the normal week
- Treating the estimate as exact
- Making a large calorie change without monitoring wellbeing
- Using an adult estimate for children, pregnancy or breastfeeding
Practical steps
- Estimate maintenance calories.
- Track intake and body-weight trend consistently for several weeks.
- Adjust gradually if the trend differs from the goal.
- Seek professional guidance for medical conditions or major dietary changes.
Run your own numbers
Use the related Fynzo tool to test different inputs and compare results.
Open the Calorie Calculator →Sources and review note
This article was reviewed for language, calculation examples and source links by Yasser Chahir, Fynzo editor. Last reviewed: July 31, 2026. It is general educational information, not medical, financial, tax or legal advice.