Project your next six menstrual cycles on a calendar grid from a single last-period date.
A free, in-browser menstrual period calendar. Enter the first day of your last period, your average cycle length, and how many days your period usually lasts — the tool projects your next six cycles on a month-by-month calendar grid so you can see at a glance when your next periods are likely to fall. Nothing is uploaded; all dates stay on your device.
Enter your LMP
Select the first day of your last menstrual period. That is day 1 of the current cycle.
Set cycle length and period duration
Cycle length is the time from the first day of one period to the first day of the next (default 28). Period duration is how many days bleeding typically lasts (default 5).
Read the calendar
Six months render side by side (stacked on mobile). Period days are shaded pink; today is outlined.
Each cycle's first day is LMP + (cycle number × cycle length). Period days fill in from that start date through the period duration you specified. The calculation assumes your cycle is regular.
Most healthy adult cycles range from 21 to 35 days, with periods lasting 2–7 days. Teens can have longer and more variable cycles for the first few years after menarche. Very short (<21 day) or very long (>35 day) cycles, or sudden changes, are worth discussing with a clinician.
Stress, travel, illness, significant weight change, intense exercise, breastfeeding, hormonal contraception changes, PCOS, thyroid disorders, and perimenopause can all shift cycles. Occasional variability is normal — persistent irregularity deserves a medical review.
No. Your LMP, cycle length, and period duration stay in your browser. The calendar is rendered entirely client-side.
Calendar projection treats the menstrual cycle as periodic, with the first day of flow recurring every cycle length days. The normal adult cycle is described in Mihm, Gangooly, and Muttukrishna (2011) as 21–35 days with bleeding typically 3–7 days. The model breaks down when cycles are irregular: intra-individual variability is common (coefficient of variation often 5–10% even in healthy women) and increases near menarche, perimenopause, with PCOS, thyroid dysfunction, and hormonal disruption. ACOG's patient FAQ on menstruation echoes the same ranges and emphasises that young people's cycles often take several years to stabilise. The tool therefore surfaces a best-case projection — useful for planning travel, medication timing, or spotting a missed period — but does not diagnose irregularity or predict the next cycle when recent cycles have varied.