Enter three numbers to generate a 12-month forecast calendar — predicted period days, fertile windows, and estimated ovulation days marked — formatted to print and pin on a wall. No account: the calendar is generated in your browser, and your three inputs are remembered in this browser (not sent to our server) so it is still there when you come back.
How this is computed: each future period is projected as last period + n × cycle length; fertile days are the 6 days ending on each estimated ovulation (predicted period − 14 days, Wilcox 1995). Limitation: the further out a month is, the more real cycles drift from any average — treat distant months as planning aids, not fixed dates.
Every month on the printout follows one pattern built from your three inputs. Here is a single Demo month, labelled:
The first day of your period counts as day 1, so the next start falls on “day 1 + cycle length” — not one day earlier:
Each later month adds the same cycle length again. The fertile window and ovulation are then counted back from each predicted start.
Small differences add up. If the cycle length you enter is off by 2 days, every month moves 2 more days away:
| Cycle | Printed date (28 days) | Actual start (30 days) | How far off |
|---|---|---|---|
| 1 | Sep 29 | Oct 1 | 2 days |
| 2 | Oct 27 | Oct 31 | 4 days |
| 3 | Nov 24 | Nov 30 | 6 days |
| 4 | Dec 22 | Dec 30 | 8 days |
| 5 | Jan 19 | Jan 29 | 10 days |
| 6 | Feb 16 | Feb 28 | 12 days |
Real cycles also vary month to month, so read the far months as approximate windows, not appointments.
Three habits keep a printed calendar close to reality:
Two or three logged start dates are enough for the cycle length calculator to give it.
A fresh first day resets every later month; a printed sheet can’t do that by itself.
The irregular period calculator shows earliest-to-latest dates rather than one day.
For a single next-period date with a countdown, use the main period calculator.
Enter last period start, cycle length, and duration above — the calendar marks predicted periods, fertile windows, and estimated ovulation for 12 months.
The math extends indefinitely; accuracy doesn't. Even regular cycles shift by a few days, so distant months are approximate windows. Nearer = more reliable. The variation comes mostly from the first half of the cycle — real-world data on 600,000+ cycles shows the luteal phase stays in a 10–15 day band while the follicular phase does the drifting, which is why one unusual month can move every later prediction.
Yes — the Print button strips everything except the 12-month calendar itself.
A single-length calendar will mislead you. Use the irregular period calculator for a date range, and treat any printed calendar as a rough sketch.
Yes — after generating, the URL encodes your three inputs. Copying the link shares the exact calendar; nothing is uploaded.
Pink = predicted period days; green = fertile window; dark green = estimated ovulation; outlined = today.
Fine for rough planning (travel, events); re-check closer to the date for anything time-critical. Never use it for contraception.
Only in this browser. Your three inputs are kept in this browser’s local storage so the calendar reappears when you come back; nothing is sent to or saved on our server. Clearing this site’s data in your browser removes them — details in the privacy policy.
Day 1 is the first day of full flow, not spotting. Count from that day 1 to the day before your next period starts — that’s one cycle length. Average it over your last 3 or more cycles. A normal adult cycle runs 24–38 days; consistently outside that range is worth discussing with a clinician.
For rough planning, yes — that’s the main reason people print one. But even a regular cycle shifts by a few days month to month, and the shift compounds the further out you go. Treat months 1–3 as fairly dependable, later months as “avoid these weeks” guidance, and re-generate with your latest period date as the event approaches.
Yes, with adjusted expectations: adolescent cycles normally run 21–45 days and are often irregular for the first few years, so distant months on the printout are rough sketches. If there’s still no first period by age 15, that’s the standard point for medical evaluation.
Not meaningfully. The pill, ring, and similar methods set their own schedule — the withdrawal bleed follows the pack, not your ovaries — so a cycle-length prediction doesn’t apply. The calendar is built for natural cycles.
It’s a good use. “When was your last period?” is one of the first questions at any gynecological visit, and this printout shows what your average predicts — a forecast, not a record of what actually happened. For a real history, log each start date in the period tracker or the printable period journal; if your shortest and longest cycles differ by more than 7–9 days over a year, that recorded spread is more useful to a clinician than any single average.