Period Calculator
28 days
5 days
Next Period--
Ovulation Date--
Knowing when your next period is due — and the several after that — helps with planning travel, events, and simply not being caught off guard. This period calculator projects upcoming menstrual start dates from the first day of your last period and your typical cycle length, listing the next six expected periods in a row. As a bonus it also marks your estimated ovulation day, since the same cycle math that predicts bleeding also predicts the fertile midpoint.
Formula
periodₙ = lastPeriod + (cycleLength × n)
- lastPeriod
- First day of your most recent period
- cycleLength
- Average days from one period’s start to the next
- n
- Which upcoming period you want (1 through 6)
How it works
- Enter the first day of your last period, your average cycle length, and your typical period length.
- Each future period start is the last period date plus a whole number of cycle lengths, so the calculator simply steps forward one cycle at a time.
- It lists the next six expected period start dates and highlights estimated ovulation at cycle length minus 14 days after your last period.
Worked example
A period began March 1, 2026, with a 28-day cycle.
- Next period: March 1 + 28 = March 29, 2026.
- Second period: March 1 + 56 = April 26, 2026.
- Third period: March 1 + 84 = May 24, 2026 (and so on through six cycles).
Upcoming periods on March 29, April 26, and May 24, 2026, with the series continuing to August 16, 2026.
Frequently asked questions
- What counts as the first day of my period?
- The first day of your period is the first day of full bleeding, not spotting. This date is the anchor for every prediction, so recording it consistently keeps your projected dates accurate.
- What is a normal cycle length?
- Most cycles run between 21 and 35 days, with 28 days as the textbook average. Cycles that fall outside that range, or that vary widely month to month, are worth discussing with a healthcare provider.
- Why does the calculator also show ovulation?
- Ovulation is estimated 14 days before your next period, so it falls naturally out of the same cycle calculation. Seeing it helps you understand your fertile timing even when your main goal is tracking your period.
- How accurate are predictions six cycles ahead?
- They assume every future cycle matches your average length exactly, so the further out a date is, the more a few days of natural variation can shift it. The nearest one or two predictions are the most dependable.