Health & fitness
Pregnancy and due-date estimate
Estimate due date and conception date from the first day of the last menstrual period.
Calculators / Health & fitness / Ovulation and period estimate
Ovulation and period estimate calculator
Estimate the next period and a likely ovulation date from a regular cycle.
On this page
Estimated next period2026-09-29
Estimated ovulation date2026-09-15
Calculator controls
How to calculate
Estimate the next period and a likely ovulation date from a regular cycle.
Next period = start + cycle length; estimated ovulation = next period − luteal phase.
Worked example
First day of latest period: 2026-09-01; Typical cycle length (days): 28; Estimated luteal phase (days): 14.
Estimated next period: 2026-09-29 ; Estimated ovulation date: 2026-09-15 .
Assumptions and limits
Cycles can vary and this estimate cannot confirm ovulation, fertility, pregnancy or contraception safety.
Results are rounded for display; calculations use unrounded values. Read our calculation methodology.
Understanding the result
Estimate the next period and a likely ovulation date from a regular cycle. The displayed figures use the inputs and formula shown on this page.
When this tool is useful
Use the ovulation and period estimate to compare a scenario, check an estimate, or verify a manual calculation.
Understanding your inputs
| Input | What to enter |
|---|---|
| First day of latest period | Enter the value in the format shown. |
| Typical cycle length (days) | Enter a number of at least 20 and no more than 45. |
| Estimated luteal phase (days) | Enter a number of at least 8 and no more than 20. |
Frequently asked questions
What should I check before using the ovulation and period estimate result?
Cycles can vary and this estimate cannot confirm ovulation, fertility, pregnancy or contraception safety.
Is this ovulation and period estimate result exact?
It is exact for the stated mathematical model and entered values. Real-world results can differ when rates, timing, fees, definitions or measurement conditions differ.