personal cycle forecast · Generated Your 6-month forecast
Predicted period days, fertile window and ovulation — based on your average cycle.
Upcoming important dates — next 12 cycles
The formula, in plain language
Count from the first day of your last period (day 1 = the first day of full flow, not spotting) and add your average cycle length. Last period on January 1 with a 29-day cycle? Expect the next one around January 30.
Everything else on this page — the calendar, the cycle-day counter, the ovulation estimate — is derived from that same anchor date, which is why getting day 1 right matters more than anything.
Don't know your cycle length?
You are in good company. Two ways out: use the helper ("Not sure what your cycle length is?") and enter a few past start dates — we average the gaps for you. Or start logging each period here; after two or three logs we offer your personal average with one tap.
Until then, 28 days is a reasonable placeholder: it is the population average, and adult cycles anywhere from 21 to 35 days are considered typical.
How accurate is the prediction?
With fairly regular cycles, calendar predictions usually land within one to two days. Accuracy fades as cycle-to-cycle variation grows — if your cycles swing by more than a week, use irregular mode for ranges instead.
Stress, illness, travel, sleep disruption and medication changes can all shift a given cycle, so treat any single prediction as a well-informed estimate, not a promise.
Beyond the date: your fertile window
The same inputs also locate your estimated ovulation (14 days before the predicted period) and the six-day fertile window ending on ovulation day. That is the window that matters if you are trying to conceive — or the one to treat with extra care if you are avoiding pregnancy, always alongside a proven contraceptive method.
How it works
Enter your last period
Pick the first day of your most recent period — the day full bleeding started, not spotting.
Set your cycle length
Not sure? Use the built-in helper: enter a few past start dates and we compute your personal average.
Get instant answers
Next period date, ovulation day, fertile window and a 6-month forecast — plus a heads-up if you're running late.
Log it, and it gets personal
When your period actually starts, come back and tap "Log this period". After two or three logs we learn your real cycle length — not the textbook 28 days — and your predictions start using it.
Frequently asked questions
How do I calculate my next period date?
Add your average cycle length to the first day of your last period. Last period August 1, cycle 28 days → next period around August 29. This page does it instantly and projects six months ahead.
What if my cycle length changes month to month?
Small swings (a few days) are normal — use your average. Swings over about a week mean irregular cycles; switch to irregular mode for range predictions, and log a few cycles to establish your true pattern.
Is the first day of spotting day 1?
No. Day 1 is the first day of full menstrual flow. Light brown spotting beforehand does not count, and using it would shift every prediction earlier.
Can I predict several months ahead?
Yes — the forecast calendar projects six months (or 3/12 with the toggle). Just remember uncertainty grows with distance; the nearest cycle is always the most reliable.
Why does my prediction differ from my app's?
Apps that learn from many logged cycles use personalized models; a calendar tool uses your stated average. Both are estimates. Logging your periods here narrows the gap.
Does this work right after stopping birth control?
Treat the first cycles after stopping hormonal contraception as settling time — they can be irregular for three to six months. Predictions become meaningful once a personal pattern re-emerges.