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, nothing saved: the calendar is generated entirely in your browser.
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.
Each cycle repeats the same pattern from your three inputs: period days marked from each predicted start for your duration; the fertile window covering the 6 days ending on estimated ovulation (14 days before each predicted period); and ovulation day itself. The nearer the month, the more reliable the marking — read months far out as approximate windows, not appointments.
For a single next-period date with a countdown and an interactive 6-month view (irregular mode included), use the main period calculator. And if your cycles vary by more than 7–9 days, start with the irregular period calculator instead of a printed calendar.
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.
No. The calendar is generated in your browser from three inputs; nothing is saved on a server.
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 a printed 12-month history answers it precisely. If your shortest and longest cycles differ by more than 7–9 days over a year, showing that spread on paper is more useful to a clinician than any single average.