What changes the calculator’s answer?
For an illustrative 30-year-old man weighing 80 kg at 180 cm, the Mifflin–St Jeor equation gives 10 × 80 + 6.25 × 180 − 5 × 30 + 5 = 1,780 calories of estimated resting energy.
| Assumption | Calculation | Estimated daily energy |
|---|---|---|
| Lower activity | 1,780 × 1.2 | 2,136 calories |
| Moderate activity | 1,780 × 1.55 | 2,759 calories |
That 623-calorie difference comes from the activity assumption alone. The decimal places in a calculator cannot remove that uncertainty. Use the result as a starting estimate, then reconsider the assumption as your routine changes.
Use the free macro calculator. Equation sources and calculator limitations. This adult example is not a calorie prescription.
Start with your maintenance calories
Maintenance is the average intake that keeps your weight broadly stable. It includes energy used at rest, daily movement, exercise and digestion. The free macro calculator estimates it from your details.
The calculator uses the Mifflin–St Jeor equation for resting energy needs, then applies an activity factor. It estimates energy use; it does not measure your metabolism.
Choose an activity level
Think about the whole day, including your job and time spent walking or sitting. Workout frequency is only a rough guide. Two people who both train three days a week may move very differently the rest of the time.
Adjust for your goal
- Maintain weight: start near the maintenance estimate.
- Lose weight: choose a manageable reduction that still supports nutrition and daily life.
- Gain weight or muscle: a modest increase may help; training matters if muscle gain is the goal.
For example, reducing an illustrative maintenance estimate of 2,200 calories by 10% gives 1,980. This shows the math, not a recommendation for every reader.
How do you know if the estimate is right?
If tracking suits you, compare your intake and weight trend over several weeks under similar conditions. Consider energy, hunger and recovery too. Water retention and menstrual-cycle changes can obscure the trend for longer than two weeks.
If the pattern consistently differs from your goal, review portions and activity before making a modest adjustment. More decimal places will not make an uncertain estimate more accurate.
Is 1,200 calories enough?
It is not a suitable default for everyone. A low target can make it hard to meet nutritional needs, especially for active or larger adults. Do not use a round number from the internet as a personal prescription.
Should you add exercise calories back?
An activity-based estimate already includes some exercise. Automatically adding a watch’s exercise estimate again can double-count it. If your activity changes substantially, review the overall target instead.
Use personal clinical advice during pregnancy, illness, eating-disorder recovery or other circumstances that change your needs. The site’s weight-planning calculator is designed for adults.