How to use the basal body temperature calculator
Prepare the values for this calculation
Summarize a series of basal body temperature readings with average, minimum, maximum, range and first-to-last change. It does not predict ovulation. 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
- Temperature unit: choose °F, °C. Match this selection to the data you enter.
- Basal temperature readings: use the same separators and value order as the example in the input table. Replace the example data with your own complete dataset.
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 Average basal body temperature first. With the unchanged example inputs, it is 97.62 °F. Compare the additional metrics with the primary result; each has its own label and unit.
Compare and keep a useful result
The result diagram shows the inputs, method and output. A numeric chart is shown only when the calculation supports a meaningful numeric relationship.
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.
Basal Body Temperature Calculator formula
Readings are converted to Celsius internally; arithmetic mean, min, max, range and last minus first are then calculated.
Inputs and units
| Input | Format / range | Example |
|---|---|---|
| Temperature unit | Select an option | °F |
| Basal temperature readings | Text / numeric list | 97.4, 97.5, 97.4, 97.8, 98.0 |
Worked example
Using the example inputs above, the average basal body temperature is 97.62 °F.
- Average basal body temperature
- 97.62 °F
- Readings
- 5
- Minimum
- 97.40 °F
- Maximum
- 98.00 °F
- Range
- 0.60 °F
- First-to-last change
- +0.60 °F
Results and assumptions
ACOG notes that BBT typically rises slightly around ovulation, but BBT alone confirms a change only after it occurs and is not a reliable standalone way to predict fertile days. Fever, illness and measurement conditions can affect readings.
Sources and method references
Fix an input or unexpected result
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.