Do you store what I enter?

No. This calculator runs locally in your browser. We do not send or store your inputs.

Can I use this as birth control?

No. These are rough estimates and are not reliable for pregnancy prevention. If you need contraception guidance, talk with a clinician.

Why don’t the dates match my actual cycle?

Cycle length can shift due to stress, illness, travel, postpartum changes, perimenopause, PCOS, and more. Use this as a starting point, not a guarantee.

What if I have irregular or long cycles?

You can still use the calculator by entering your best average. If your cycles are frequently very short or very long (or you’re worried), consider checking in with a clinician.

Period & Cycle Calculator

Use this free period and cycle calculator to estimate upcoming period dates and where you are in your current cycle. Enter the first day of your last period plus your typical cycle and period length. You can optionally enable TTC estimates for ovulation and fertile window.

Privacy note: this tool runs locally in your browser. We don’t send or store what you enter.

Enter your last period start date to see estimated upcoming dates.

How it works

We treat the first day of your last period as cycle day 1.
We add your average cycle length to estimate your next period start dates.
We estimate a period “end date” by adding your average period length.
If TTC estimates are enabled, we estimate ovulation as (cycle length − luteal phase length) and show a fertile window from 5 days before ovulation through ovulation.

Notes

All results are informational estimates only. Cycles naturally vary month to month.
This is not medical advice. If you have concerns or very irregular cycles, consider talking with a clinician.
TTC estimates are not a guarantee of pregnancy and are not birth control.

FAQ

Do you store what I enter?: No. This calculator runs locally in your browser. We do not send or store your inputs.
Can I use this as birth control?: No. These are rough estimates and are not reliable for pregnancy prevention. If you need contraception guidance, talk with a clinician.
Why don’t the dates match my actual cycle?: Cycle length can shift due to stress, illness, travel, postpartum changes, perimenopause, PCOS, and more. Use this as a starting point, not a guarantee.
What if I have irregular or long cycles?: You can still use the calculator by entering your best average. If your cycles are frequently very short or very long (or you’re worried), consider checking in with a clinician.

Sources

Support

If something doesn’t look right, remember these are estimates. You can reach us via support.

More tools

Browse all free tools on the tools index.