Luteal Phase Calculator
Calculate luteal-phase length from an observed/estimated ovulation date and next period start.
Enter or adjust the values above, then calculate.
Luteal Phase: days from Ovulation to Period
Calculate luteal-phase length from an observed/estimated ovulation date and next period start.
Inputs this tool uses
- Ovulation date
- Next period start
What you get
Days between entered ovulation and next period start.
How to use the Luteal Phase Calculator
- Enter ovulation date, next period start.
- Select any method, activity level or option shown on this page, then choose Calculate.
- Read the main result together with the supporting values, method, assumptions and limitations below before using the estimate.
How this calculation works
Cycle tools use date arithmetic from observed period starts and user-entered cycle assumptions. Estimates are never presented as contraception.
Example calculation
The sample values loaded into the calculator produce 0 days. This example exists to show how the output is structured; replace the sample values with your own inputs for your calculation.
Assumptions and limitations
- Cycle and ovulation dates are estimates and can vary from cycle to cycle.
- This tool is not contraception and does not diagnose fertility or pregnancy.
Sources and review status
Source set last verified 2026-09-25. No clinician review is claimed unless a real named reviewer is displayed.
Connected tools
Continue with the closest related calculation without re-entering sensitive values automatically.
Estimate ovulation from the expected next period minus an editable luteal-phase assumption and show the assumption used.
Open tool →◌Fertile Window CalculatorEstimate a broad fertile window around ovulation and explicitly state that the result is not contraception.
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Open tool →