Lunia · Free tools
Luteal Phase Calculator
Count the interval between an estimated ovulation date and the next period.
Your details
Runs entirely in your browser. Nothing you type is sent anywhere or saved.
Your result
Ready to calculate
Enter your details, then calculate to see your result here.
How this calculator works
The calculator subtracts the ovulation date from the first day of the following period using calendar days. An interval after estimated ovulation is shown, rather than claiming to measure progesterone or confirm an ovulatory cycle.
A worked example
Estimated or observed ovulation date: Aug 16, 2026 · First day of the following period: Aug 30, 2026
- Interval after estimated ovulation
- 14 days
- Dates used
- Aug 16, 2026 to Aug 30, 2026
These are illustrative inputs, not personal recommendations.
Common questions
Can a calendar confirm my luteal phase?
No. A calendar can count an interval between dates you enter. It cannot determine the biological moment of ovulation or assess hormone levels.
How should I use the result?
Ovulation dates from apps, LH tests and temperature observations have different uncertainty. A date interval cannot diagnose a luteal-phase condition or confirm ovulation. Discuss concerns with a qualified clinician.
Sources & method references
Formula-based results are estimates, not individual medical advice.