Track your menstrual cycle and predict your next period, plus up to 3 future cycles, with optional fertile window and ovulation estimates.
Track your menstrual cycle and predict your next period. This calculator provides estimates based on your cycle history, is for informational purposes only, and should not be used as a form of birth control.
Cycle Information
days
days
days
Tracking Options
Your Predicted Cycles
Current Cycle
Expected Period
Aug 4 – Aug 8
Expected Ovulation
Tue, August 18, 2026
Fertile Window
Aug 13 – Aug 19
Cycle 2
Expected Period
Sep 1 – Sep 5
Expected Ovulation
Tue, September 15, 2026
Fertile Window
Sep 10 – Sep 16
Cycle 3
Expected Period
Sep 29 – Oct 3
Expected Ovulation
Tue, October 13, 2026
Fertile Window
Oct 8 – Oct 14
Cycle 4
Expected Period
Oct 27 – Oct 31
Expected Ovulation
Tue, November 10, 2026
Fertile Window
Nov 5 – Nov 11
Disclaimer: This calculator provides estimates based on your cycle history and is for informational purposes only, not a diagnosis. Do not use this tool as a form of birth control (contraception). Talk to your healthcare provider if you have concerns about your cycle.
Last updated: July 2026
Understanding Your Menstrual Cycle
Tracking your period can help with everything from planning around an upcoming trip to understanding your body better. This calculator uses the first day of your last period, your average cycle length, and your period length to forecast your next period — plus up to 3 cycles beyond that — along with optional fertile window and ovulation estimates. It's an estimate based on averages, not a diagnosis or a form of contraception; talk to your healthcare provider about anything cycle-related that concerns you.
The Phases of Your Cycle
Menstruation (the period): Day 1 of your cycle. The uterine lining sheds, causing bleeding, typically lasting 3–7 days.
Follicular phase: starts on Day 1 and overlaps with your period, as your body prepares to release a new egg. This phase varies the most in length from person to person.
Ovulation: a mature egg is released from the ovary, usually around Day 14 in a 28-day cycle.
Luteal phase: after ovulation, the body prepares for a potential pregnancy. If the egg isn't fertilized, hormone levels drop and trigger the next period. This phase is close to 14 days for most people.
How the Calculator Works
Starting from the first day of your last period, the calculator adds your average cycle length to predict each upcoming period. Because the luteal phase is fairly fixed, it counts back roughly 14 days from each predicted period to estimate ovulation, then sets the fertile window as the 5 days before ovulation through the day after — matching how long sperm and an egg can each survive.
A Worked Example
Say your last period started March 1, your average cycle is 28 days, and your period lasts 5 days:
Current Cycle: period March 1–5, ovulation around March 15, fertile window March 10–16
Cycle 2 (next period): period March 29 – April 2, ovulation around April 12, fertile window April 7–13
Cycle 3: period April 26–30, ovulation around May 10, fertile window May 5–11
Note how each cycle shifts a little further out — that's expected, since every prediction builds on your average cycle length rather than a guaranteed fixed date.
Frequently Asked Questions
A normal menstrual cycle can range anywhere from 21 to 35 days. The global average is often cited as 28 days, but it's completely normal for your cycle to be shorter or longer, as long as it's fairly consistent for you.
The luteal phase is the second half of your menstrual cycle, starting the day after ovulation and ending the day before your next period begins. Unlike the first half of your cycle, which can vary a lot, the luteal phase is far more consistent — close to 14 days for most people.
No. Never use a calendar-based period calculator as a form of contraception. Cycles can fluctuate due to stress, illness, travel, or weight changes, meaning ovulation can happen earlier or later than predicted, and this tool cannot account for that variation.
This Period Calculator is built for broader cycle tracking — it forecasts your next period plus up to 3 future cycles, with fertile window and ovulation shown as optional add-ons you can toggle. The Ovulation Calculator is narrower and specifically built around trying to conceive, centering the fertile window for your current cycle. If you want a multi-month calendar view, use this page; if you're focused on this cycle's conception timing, the Ovulation Calculator is the more direct tool.
Each future prediction in this calculator is built on the one before it, using your average cycle length. Because real cycles vary somewhat month to month, predictions further in the future carry more uncertainty than your very next period.
Yes. Many people track their cycle to anticipate PMS symptoms, plan travel or events around their period, monitor for irregularity that's worth discussing with a doctor, or simply understand their own patterns better.
A single late period is common and often not a cause for concern, but if your cycles are consistently irregular, or a period is very late and you might be pregnant, it's worth talking to a healthcare provider or taking a pregnancy test rather than relying on calendar predictions alone.