LMP Apr 1, 2026, 28 day cycle
- Fertile window
- Apr 10, 2026-Apr 15, 2026
- Next period
- Apr 29, 2026
- Luteal phase
- 14 days
Ovulation Calculator
Use this free ovulation calculator to estimate ovulation date, fertile window, and next period from last period and cycle length.
Estimate, not diagnosisFormula notesExample inputsTab-only history
Formula steps
- Estimate the next period from the last period date and cycle length.
- Subtract the luteal phase length to estimate ovulation.
- Show the fertile window as the five days before ovulation through ovulation day.
Examples
Recent answers
Recent ovulation estimates will appear here.
Calendar ovulation estimates work best with regular cycles and are not contraception.
Inputs and recent answers stay in this browser tab and are not sent to a server.
How to use the Ovulation Calculator
- Enter the requested measurements, dates, lab values, or workout details.
- Check that the units and formula assumptions match what the tool is asking for.
- Press the calculate button to see the answer, supporting metrics, and formula steps.
- Read the estimate with the health disclaimer in mind, then copy the result if you need it for notes.
What people use it for
Estimate ovulation for regular cycles.
See the fertile window around ovulation.
Plan cycle tracking with a luteal phase assumption.
Avoid using calendar estimates as contraception.
Quick examples
28-day cycle
LMP Apr 1, 2026, cycle 28, luteal 14Ovulation Apr 15; fertile window Apr 10-Apr 15; next period Apr 29
30-day cycle
LMP Apr 4, 2026, cycle 30, luteal 14Ovulation Apr 20; fertile window Apr 15-Apr 20; next period May 4
26-day cycle
LMP Apr 10, 2026, cycle 26, luteal 12Ovulation Apr 24; fertile window Apr 19-Apr 24; next period May 6
Fertile window
Five days before ovulation through ovulation dayPlanning window, not a guarantee
Need the guide or a nearby tool?
Need a slower walkthrough, a related calculator, or the full library? These links keep you close to the task you started.
- How to use the Ovulation CalculatorSee slower examples, input meanings, formula notes, result limits, and mistakes to avoid.
- Health & FitnessBrowse related calculators and utilities in the same category.
- Calculator and utility guidesFind more guides that use real tool inputs and example numbers.
- All free toolsSearch every live tool, converter, calculator, AI helper, and browser utility.
Frequently asked questions
Plain-language answers about when to use the estimate, what the formula means, what it cannot decide for you, and how privacy works.
When should I use the Ovulation Calculator?
Use it for simple educational checks, trend tracking, or planning tasks like these: Estimate ovulation for regular cycles. See the fertile window around ovulation. It can help you understand a number, but it cannot explain your whole health situation.
What do the main Ovulation Calculator inputs mean?
Enter the first day of the last period, your usual cycle length from one period start to the next, and luteal phase length if you know it. If you do not know luteal phase length, keep the 14-day default and read the answer as a calendar estimate for regular cycles, not a confirmed ovulation test.
What is the Ovulation Calculator doing with my inputs?
In plain language: The calculator estimates next period as last period date plus cycle length, estimates ovulation as next period minus luteal phase length, and shows the fertile window as the five days before ovulation through ovulation day. Read the result together with the notes on the page, because health and fitness numbers often need personal context.
How should I read the Ovulation Calculator result?
Read the ovulation date as the center of a calendar estimate, not proof that ovulation will happen that day. The fertile window is the five days before estimated ovulation through ovulation day because sperm can survive for several days and the egg survives for about a day after release.
Why does the calculator ask for luteal phase?
The luteal phase is the part of the cycle after ovulation and before the next period. Many quick calendars assume 14 days, but some people track a different pattern. The calculator subtracts that number from the expected next period to estimate ovulation.
What if my cycles are irregular?
Calendar estimates are less reliable when cycles vary a lot, periods are missing, you recently stopped hormonal birth control, you are postpartum, or illness, stress, travel, or medication changed the cycle. Use the result as a rough planning note, not proof.
Is the fertile window the same as ovulation day?
No. Ovulation day is the estimated egg-release day. The fertile window is wider because sperm can survive for several days before ovulation and the egg survives for about a day after ovulation.
Can I use this calculator as contraception?
No. A simple calendar estimate is not reliable contraception by itself. If preventing pregnancy matters, use evidence-based contraception guidance from a qualified health professional.
Can I use this as medical advice?
No. This page provides an educational estimate only. Talk with a qualified health professional before making medical, pregnancy, nutrition, medication, or safety decisions. Use the calculator as a learning tool, then ask a qualified professional about decisions that affect care, pregnancy, medication, nutrition, or safety.
What should I double-check before trusting the result?
Check that the date is the first day bleeding started, that cycle length means period start to next period start, and that luteal phase is in days. Do not enter period length, suspected ovulation date, or a positive test date into the last-period field.
Does the site save my health inputs?
No. The calculator runs in your browser tab. Recent answers stay only on the page while you use it, and they are not sent to a server.