Period Calculator
Next-period and fertile-window calendar sketch from LMP — related to ovulation tracking, not a clinic workup. Click any i for detail.
Cycle
First day of last period
i
LMP
Day 1 of bleeding for your most recent period. |
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|---|---|
Average cycle length (days)
i
Cycle
Days from day-1 to next day-1. 28 is common. |
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Luteal length (days)
i
Luteal
Days from ovulation to next period. Default 14. |
How to use this calculator
- Enter the first day of your last period.
- Set typical cycle length (and luteal length if known).
- Read the next-period date and fertile-window sketch.
- See the ovulation calculator when you want ovulation-day emphasis.
Results explained
Next period is sketched as LMP plus cycle length. Ovulation is placed about luteal-length days before that period, and the fertile window usually spans roughly five days before ovulation through the day after. Irregular cycles, stress, and PCOS break fixed arithmetic — treat this as a calendar aid, not contraception or infertility care.
Quick reference: period timing
Next period ≈ LMP + cycle; fertile window sits around ovulation.
| Item | Detail |
|---|---|
| 28-day cycle | Next period in 28 days; ovulation ~ day 14 if luteal=14 |
| Fertile window | About ovulation − 5 through ovulation + 1 |
| Short cycles | Everything shifts earlier |
| Confirmation | OPKs, temps, or clinician guidance |
Educational only — not birth control advice and not a pregnancy test.
How the estimate is built
next_period = LMP + cycle_length; ovulation_day = cycle − luteal; fertile ≈ [ovulation − 5, ovulation + 1].
Example scenario
LMP March 1, 28-day cycle → next period ~ March 29, fertile ~ March 10–16 if luteal=14.
FAQ
How is this different from the ovulation calculator?
Same cycle math family — this page leads with next period, while ovulation leads with ovulation day. Related inputs, different emphasis.
Can I use this as contraception?
No. Calendar methods fail without training and perfect use.
What if spotting starts early?
Many people still count day 1 as full flow. Follow the definition your clinic uses.
Why adjust luteal length?
If you chart a shorter luteal phase, ovulation estimates move later relative to the next period.