Lifestyle
Food & Nutrition
FitnessPredict your next periods and see your cycle at a glance.
This tool is for general information only and is not medical advice. Talk to a healthcare professional about results that concern you.
How the Period Calculator Works
Your cycle starts on the first day of one period and ends the day before the next one begins. Enter that start date, your average cycle length, and how long your period usually lasts, and the calculator maps out your next six cycles: when each period should start, how long it should run, and your estimated ovulation day in between.
A cycle anywhere from 21 to 35 days is considered normal for adults, and it is completely normal for the length to drift by a couple of days from month to month. The predictions here assume your average holds, so treat them as a solid planning guide rather than a guarantee.
Why Track Your Cycle?
- No surprises: know before trips, events, and big days
- Spot changes early: a cycle that suddenly shortens, lengthens, or disappears is information your doctor can use
- Understand symptoms: PMS, cramps, energy dips, and skin changes all follow the cycle
- Plan or avoid pregnancy: ovulation timing is the key input either way
If you are trying to conceive, the ovulation calculator goes deeper on your fertile window, and if your period is late, the due date calculator is the next stop.
Frequently Asked Questions
Why is my period late?
Stress, travel, illness, weight change, heavy training, and new medication can all delay ovulation, which delays the period that follows. Pregnancy is the other obvious cause. One late period is rarely a concern; a pattern of missed periods is worth a doctor visit.
What counts as an irregular cycle?
Cycles that vary by more than 7 to 9 days from month to month, or fall outside the 21 to 35 day range. Occasional irregularity is normal, especially in the teens and during perimenopause. Consistent irregularity deserves a checkup.
How accurate is a period calculator?
For people with steady cycles, usually within a day or two. The further ahead you look, the more small variations add up, so the six month view is for planning, not precision.
Can I get pregnant right after my period?
With short cycles, yes. Sperm survive up to five days, so sex in the days after a period can overlap an early ovulation. If avoiding pregnancy, do not rely on calendar math alone.
Sources
- The Menstrual Cycle: Menstruation, Ovulation, and How Pregnancy Occurs · ACOG
- Menstrual Cycle (Normal Menstruation): Overview & Phases · Cleveland Clinic
- Menstruation | Period | MedlinePlus · MedlinePlus
- Your First Period · ACOG
This calculator is for general information only and is not a substitute for medical advice or contraception.