Period Tracker
What this Period Tracker does
This tracker estimates your next period, predicted ovulation, and a fertile window based on your last period date, your average cycle length, and (optionally) your luteal phase. It’s an estimate—not a diagnosis—and real cycles can vary.
All calculations run in your browser; no data is stored or sent.
How the tool works
- Enter the first day of your last period.
- Enter your average cycle length (common range: 21–35 days).
- Optionally add your typical period length and luteal phase (defaults to 14 days if blank).
- Press Calculate to see your next period, ovulation estimate, and fertile window, plus a multi-cycle forecast.
What to enter
- Last period start: first day bleeding began (not light spotting).
- Cycle length: days from Day 1 of one period to Day 1 of the next.
- Period length: number of bleeding days (optional, used for range display).
- Luteal phase: days between ovulation and next period (optional; default 14).
Tip: If your cycle length varies, use a recent average (e.g., mean of last 3–6 cycles).
How dates are estimated
Next period
Next Start ≈ Last Start + Cycle Length
Range uses period length if provided.
Ovulation
Ovulation ≈ Last Start + (Cycle Length − Luteal Phase)
If luteal is blank, we assume 14 days.
Fertile window
Fertile Window ≈ Ovulation − 5 days → Ovulation + 1 day
Sperm can survive up to ~5 days; the egg ~24 hours.
Understanding your cycle
Timing can vary per person and from cycle to cycle.
Helpful tips
- Track a few cycles to find your average cycle length.
- Note changes due to travel, stress, illness, or new medication.
- Record symptoms (cramps, mood, discharge) to learn your patterns.
Common mistakes
- Using spotting as Day 1 (use first day of full flow).
- Mixing calendar months with cycle days—count days, not dates.
- Assuming ovulation is always Day 14 (it varies by person).
Frequently asked questions
My cycles are irregular—will this still help?
Yes, as a rough guide. A wider fertile window may be shown if you vary a lot. If cycles are very irregular or absent, consider speaking with a healthcare professional.
Can this predict pregnancy?
No. It only estimates likely fertile days. For conception timing, combine with ovulation tests and symptom tracking.
What if I miss a period?
Take a pregnancy test if relevant and/or consult a professional—missed periods can have many causes (stress, illness, thyroid issues, PCOS, lifestyle shifts).
Is my data saved?
No. This page does not store or send your inputs. Everything stays in your browser session.
Important note
This tool provides estimates and is not medical advice. If you have concerns (e.g., very painful periods, heavy bleeding, missed periods), please consult a qualified healthcare provider.