How to use the metabolic age calculator
Prepare the values for this calculation
Solve the age term in the Mifflin–St Jeor equation that corresponds to an entered measured/estimated resting energy value. This is a mathematical reference age, not biological age. Use the formula below to check that it answers your question. Read the input units before transferring figures from a statement, measurement or dataset.
Enter and check each input
- Sex used by equation: choose Male, Female. Match this selection to the data you enter.
- Weight (kg): enter a value at least 20 and no more than 400. Use the unit named in the label or selected above. Do not leave this required field blank.
- Height (cm): enter a value at least 80 and no more than 250. Use the unit named in the label or selected above. Do not leave this required field blank.
- Measured/estimated resting energy (kcal/day): enter a value at least 100. Use the unit named in the label or selected above. Do not leave this required field blank.
The input table gives a complete example. Keep units and time periods consistent across related fields.
Calculate and resolve any input error
Choose Calculate after entering the values. Changes also update the answer after a short pause. If an error appears, follow its message, correct the field and calculate again. Reset restores the example values.
Interpret the answer
Check Mifflin-equivalent age first. With the unchanged example inputs, it is 29.8 years. Interpret it using the formula and assumptions on this page.
Compare and keep a useful result
For a controlled comparison, keep every other example input unchanged and change Weight (kg) from 75 to 82.5. The resulting Mifflin-equivalent age is 44.8 years. This illustrates the equation’s response to that input, rather than a forecast of real events.
Read the chart’s axis labels and data table. A scenario curve changes one stated input while holding the others fixed; it does not add external observations. Use Download graph to save an available chart as a PNG.
Use Copy result or Download CSV to keep the answer. Share tool shares the page address without placing your input values in the URL. Recheck inputs and assumptions before using the result for a decision.
Metabolic Age Calculator formula
Age is algebraically solved from the Mifflin–St Jeor BMR equation for the entered sex, height, weight and BMR.
Inputs and units
| Input | Format / range | Example |
|---|---|---|
| Sex used by equation | Select an option | Male |
| Weight (kg) | minimum 20; maximum 400 | 75 |
| Height (cm) | minimum 80; maximum 250 | 175 |
| Measured/estimated resting energy (kcal/day) | minimum 100 | 1700 |
Worked example
Using the example inputs above, the mifflin-equivalent age is 29.8 years.
- Mifflin-equivalent age
- 29.8 years
Results and assumptions
This is only the age term that makes the Mifflin–St Jeor equation equal the entered BMR. It is not biological age, a diagnosis, or a validated health-age score.
Fix an input or unexpected result
Weight (kg) is required. Enter weight (kg) using the format and bounds in the input table. Zero and an empty field are different: use zero only if it is allowed and represents your data.
If your answer differs from the example, choose Reset and compare every field, including selected units and options. Check percentage versus decimal entry and whether values describe the same period. Round only the final displayed answer when reproducing the formula.
If a discrepancy remains, report the calculator issue with the page address, non-sensitive example inputs, actual result, expected result and a reference for your calculation.