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Ovulation and fertile window calculator

When am I most fertile?

When ovulation is likely and which days matter, worked back from your own cycle length rather than assuming 28 days.

Your usual cycle length

days

First day of one period to the first day of the next

Luteal phase length

days

Leave at 14 unless a doctor has measured yours

Day of your cycle today

day

Day 1 is the first day of full flow

These are example numbers. Replace them with yours, then press Calculate.

Example answer

14day of cycle

day 13-17

The range most cycles fall into. Sperm survive up to about five days, so intercourse every one to two days across the window matters more than hitting one exact day.

This is a guide, not a diagnosis. Share the result with your doctor.

Your result on the scale

The ranges this calculator uses. Yours is highlighted.

Your numbers

Everything worked out from what you entered.

Likely ovulation: day 14 of your cycle
Fertile window: day 9 to day 15
Best days to try: day 12 to day 14
From today: 13 day(s) away
Next period due: day 29, about 28 day(s) away

What each result means

Your result is highlighted. Your own clinic's advice always comes first.

Your resultbefore day 10

Very early ovulation. Often goes with a short cycle and can leave the follicle less time to mature. Worth raising if cycles are consistently under 24 days.

Your resultday 10-12

Earlier than average but common in shorter cycles, and compatible with conception.

Your resultday 13-17

The range most cycles fall into. Sperm survive up to about five days, so intercourse every one to two days across the window matters more than hitting one exact day.

Your resultday 18 or later

Late ovulation, usual in longer cycles. If cycles are long or unpredictable, PCOS and thyroid function are the two things normally checked first.

Where this fits in your journey

The usual order, from trying to conceive to pregnancy. Not everyone needs every stage. This calculator belongs to stage 1.

Stage 1 · you are here

Trying to get pregnant

Timing and the basics, before any treatment.

This calculator: When am I most fertile?

Calculators for what comes next

How this is worked out

Date calculationExact arithmetic on the dating convention named below. Scan dating by your clinic takes precedence.

Ovulation is estimated by counting back from the next expected period, not forward from the last one. The luteal phase is the more stable half of the cycle, so counting back is more reliable when cycle length varies.

About this calculator

?What it tells you

Your best days to try this month. When ovulation is likely and which days matter, worked back from your own cycle length rather than assuming 28 days.

✓When to use it

Every cycle while trying to conceive

iWhat you need

Your usual cycle length (days)
Luteal phase length (days)
Day of your cycle today (day)

!What it cannot tell you

Estimated from cycle length, not measured. An LH test or follicle tracking confirms what actually happened in a given cycle.

Common questions

Why count back instead of forward?

The luteal phase, from ovulation to the next period, is more consistent than the first half. If your cycle runs to 33 days, ovulation is nearer day 19 than day 14, and counting forward from your period would miss the window entirely.

My cycles are irregular. Is this useful?

Less so. If your cycle length varies by more than a few days, the window this produces is wide. Ovulation predictor kits or follicle tracking are more reliable, and irregular cycles are themselves worth investigating.

Does a positive ovulation test mean I definitely ovulated?

No. The test detects the LH surge, which normally triggers release. In luteinized unruptured follicle syndrome the surge happens and the egg is never released. Only ultrasound can tell the difference.

Sources

Estimates only. Ovulation moves between cycles even in regular ones, and this calculation assumes a consistent luteal phase. An LH test, a mid-luteal progesterone, or follicle tracking measures what actually happened in a given cycle. It is not a contraceptive method.

In an emergency

If you have any of the warning signs listed here, don't wait for a test result or a calculator. Get help now.

112All emergencies, anywhere in India 108Ambulance

Also call your IVF clinic. Most clinics give an emergency number on your treatment or discharge sheet. Save it in your phone now, before you need it.