Life Tools

Ovulation Calculator

Find your ovulation date, fertile window, and next period based on your cycle. Covers the next 3 cycles so you can plan ahead. Completely private — nothing leaves your browser.

100% private — no data storedFree & no signup

Your cycle

First day of last period

Cycle length (days)

Typical: 21–45 days

Period length (days)

Typical: 3–7 days

View cycle

days to ovulation

days to next period

PeriodFertile windowOvulation dayNormal

Cycle 1 — key dates

Period

May 9, 2026 – May 13

5 days

Fertile window

May 18, 2026 – May 24

7 days — highest chance of conception

Ovulation day

May 23, 2026

Peak fertility — egg viable ~24 hours

Next period

Jun 6, 2026

Cycle timeline — day by day

PeriodDay 1–5 · May 9 – May 13

Fertile windowDay 10–16 · May 18 – May 24

OvulationDay 15 · May 23

3-cycle overview

Cycle	Period starts	Fertile window	Ovulation	Next period
Cycle 1	May 9, 2026	May 18 – May 24	May 23, 2026	Jun 6, 2026
Cycle 2	Jun 6, 2026	Jun 15 – Jun 21	Jun 20, 2026	Jul 4, 2026
Cycle 3	Jul 4, 2026	Jul 13 – Jul 19	Jul 18, 2026	Aug 1, 2026

⚠️ Medical disclaimer

This calculator uses the standard calendar method and assumes a regular cycle. It is not a substitute for medical advice, ovulation tests, or fertility treatment. Irregular cycles reduce prediction accuracy. Consult a healthcare provider for fertility planning.

How to use the ovulation calculator

Three inputs, three cycles of predictions — takes under a minute.

01
Enter the first day of your last period
This is day 1 of your cycle — the first day of actual bleeding, not spotting. If you're not sure of the exact date, use your best estimate.
02
Set your cycle and period length
The average cycle is 28 days (range: 21–45). Period length is typically 3–7 days. If your cycle varies, use your average over the last 3–6 months.
03
Read your fertile window and ovulation date
The calculator shows your period, fertile window, ovulation day, and next period start for 3 upcoming cycles. Switch between cycles using the tabs.

What people use this for

Trying to conceive

The fertile window (5 days before ovulation + ovulation day) is when conception is most likely. Sperm can survive up to 5 days, so timing intercourse in this window maximises the chance.

Tracking your cycle for general health

Knowing when your period is due helps with planning, managing PMS symptoms, and spotting irregularities. A cycle that's consistently shorter than 21 days or longer than 45 days is worth discussing with a doctor.

Natural family planning

The calendar method can be used to identify fertile days to avoid. It's less reliable than hormonal contraception — typical use failure rate is around 24% per year — and works best with regular cycles.

Preparing for a fertility appointment

Doctors often ask for cycle history. Having 3–6 months of cycle data — start dates, length, period duration — makes the appointment more productive.

Frequently asked questions

Free, no account needed. Nothing is stored or sent anywhere.

It uses the standard calendar method: ovulation is estimated at cycle length minus 14 days. For a 28-day cycle that's day 14. Accuracy drops with irregular cycles — a 3-day variation in cycle length shifts the ovulation estimate by 3 days.

The luteal phase (ovulation to next period) is consistently about 14 days in most women. The follicular phase (period to ovulation) varies. So ovulation = next period minus 14 days.

The 7-day window from 5 days before ovulation to 1 day after. Sperm can survive up to 5 days in the reproductive tract, and the egg is viable for about 24 hours after ovulation.

The calendar method alone is not reliable contraception. Typical use failure rate is around 24% per year. For contraception, use a medically approved method.

Irregular cycles make calendar-based predictions less accurate. Track your cycle for 6+ months to find your average, or use ovulation predictor kits (OPKs) which detect the LH surge directly.

Yes. Significant stress, illness, travel, or weight changes can delay or suppress ovulation, shifting it away from the predicted date.

Nothing is sent to any server. The calculation runs entirely in your browser.

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Cycle

Period starts

Fertile window

Ovulation

Next period

Cycle 1

May 9, 2026

May 18 – May 24

May 23, 2026

Jun 6, 2026

Cycle 2

Jun 6, 2026

Jun 15 – Jun 21

Jun 20, 2026

Jul 4, 2026

Cycle 3

Jul 4, 2026

Jul 13 – Jul 19

Jul 18, 2026

Aug 1, 2026

How to use the ovulation calculator

Three inputs, three cycles of predictions — takes under a minute.

Enter the first day of your last period

This is day 1 of your cycle — the first day of actual bleeding, not spotting. If you're not sure of the exact date, use your best estimate.

Set your cycle and period length

The average cycle is 28 days (range: 21–45). Period length is typically 3–7 days. If your cycle varies, use your average over the last 3–6 months.

Read your fertile window and ovulation date

The calculator shows your period, fertile window, ovulation day, and next period start for 3 upcoming cycles. Switch between cycles using the tabs.

What people use this for

Trying to conceive

The fertile window (5 days before ovulation + ovulation day) is when conception is most likely. Sperm can survive up to 5 days, so timing intercourse in this window maximises the chance.

Tracking your cycle for general health

Natural family planning

Preparing for a fertility appointment

Doctors often ask for cycle history. Having 3–6 months of cycle data — start dates, length, period duration — makes the appointment more productive.

Frequently asked questions

Free, no account needed. Nothing is stored or sent anywhere.

The luteal phase (ovulation to next period) is consistently about 14 days in most women. The follicular phase (period to ovulation) varies. So ovulation = next period minus 14 days.

The 7-day window from 5 days before ovulation to 1 day after. Sperm can survive up to 5 days in the reproductive tract, and the egg is viable for about 24 hours after ovulation.

The calendar method alone is not reliable contraception. Typical use failure rate is around 24% per year. For contraception, use a medically approved method.

Irregular cycles make calendar-based predictions less accurate. Track your cycle for 6+ months to find your average, or use ovulation predictor kits (OPKs) which detect the LH surge directly.

Yes. Significant stress, illness, travel, or weight changes can delay or suppress ovulation, shifting it away from the predicted date.

Nothing is sent to any server. The calculation runs entirely in your browser.