Period Calculator and Cycle Tracker
Free period calculator and cycle tracker: see when your next period is due, the next 12 months, your fertile days, and log your cycles to get your own average and how regular you are. Private, no sign-up, adds to your phone calendar.
🔒 Private by design: your dates are saved only in this browser (never uploaded, no account) and are shared by the three calculators below.
More options: period length, luteal phase, ovulation (LH) test
Your chances, day by day
Chance of pregnancy from sex on each day, for a typical couple. The two days before ovulation and ovulation day are the peak. Source: Wilcox, Weinberg & Baird, New England Journal of Medicine 1995 (129 couples, 625 cycles). Ovulation can move by a few days, which is why the whole window counts.
Your cycle log
Add the first day of each period you remember. With two or more, the calculator uses your own average instead of the textbook 28 days, and tells you how regular you are.
Upcoming periods
Calendar
Tap a day for details.
Next six cycles
Key dates
Week-by-week calendar (weeks 1–42)
Day by day after ovulation
Week by week
These are estimates from averages, not medical advice or contraception. Bodies vary and cycles change with stress, illness, breastfeeding and age. Talk to a doctor or midwife about your own situation, especially if your cycles are very irregular or you have been trying for 12 months (6 if you are over 35).
Period calculator and cycle tracker
Find out when your next period is due, see the following twelve months at a glance and keep a simple log of your cycles. Enter the first day of your last period; add earlier periods to the log and the calculator replaces the textbook 28 days with your own average, shows how regular you are and gives a range of dates when your cycles vary.
What you get
- Next period date and the length of the period, with a possible date range from your shortest and longest cycles.
- A late period notice that counts the days and points to the pregnancy-test and due-date tools.
- A cycle log with your average, shortest, longest and how much your cycle length swings.
- A calendar showing periods, the fertile window and ovulation days, plus the next six cycles in a table.
- Add expected periods to your phone calendar (.ics file).
- Free, private, no sign-up: your log is stored only in this browser. Use “Copy log” to back it up.
Questions
How is my next period predicted?
It is the first day of your last period plus your cycle length. If you log two or more periods, your average of the last six cycles is used.
What is a normal cycle length?
For adults, 21 to 35 days is considered normal, and the length can vary by a few days from month to month. Teenagers' cycles can be longer, and cycles often become shorter and less regular in the years before menopause.
Why is my period late?
Pregnancy is one reason, but stress, illness, travel, big changes in weight or exercise, breastfeeding, thyroid problems and conditions such as PCOS can all delay a period. If you could be pregnant, take a test from the first day of the missed period. See a doctor if you miss three periods in a row or your cycles suddenly change.
Is it a problem if my cycle is irregular?
Cycles that differ by more than 7–9 days from month to month, or that are shorter than 21 or longer than 38 days, are worth discussing with a doctor. A log like this one gives them useful information.