Period Calculator
Track your cycle, predict ovulation, and find your fertile window – all in one place.
Understanding Your Menstrual Cycle
A typical menstrual cycle lasts between 21 and 35 days, with 28 days being the average. The cycle is counted from the first day of your period to the day before your next period starts. Knowing your cycle length helps you anticipate your next period, ovulation, and your most fertile days.
Ovulation usually occurs about 14 days before your next period. If you have a 28‑day cycle, you likely ovulate around day 14. The fertile window – the days when pregnancy is possible – includes the five days before ovulation plus the day of ovulation itself.
How to Use the Period Calculator
- Enter the first day of your last period – use the date picker.
- Set your average cycle length – the default is 28 days, but you can adjust it (20–45 days).
- Choose your typical period duration – how many days your bleeding usually lasts (1–10 days).
- Click “Calculate My Cycle” to see your next period dates, ovulation day, fertile window, and the best day for a pregnancy test.
The tool works entirely in your browser – no data is ever stored or shared. You can use it as often as you like, completely free.
Frequently Asked Questions
Is the ovulation prediction accurate?
The calculator estimates ovulation based on a regular cycle. For most women with consistent cycles, it’s a reliable guide. However, stress, illness, or hormonal changes can shift ovulation. If you’re trying to conceive, consider combining this tool with ovulation test kits or basal body temperature charting.
Can I use this calculator if my cycles are irregular?
Yes, but the predictions will be less accurate. Enter the average length of your last few cycles for a better estimate. If your cycles vary by more than 7–9 days, speak with a healthcare provider for personalised advice.
What if I don’t know my cycle length?
Start with the default 28 days. Track your periods for 3–4 months (using a diary or an app), then return and enter your real average. The more data you provide, the more accurate the tool becomes.
Does this replace a doctor’s advice?
No. This calculator is for informational and educational purposes only. It’s not a medical diagnosis. If you have concerns about amenorrhea, severe pain, or very irregular cycles, please consult a qualified health professional.
Disclaimer: This period calculator provides estimates based on a regular cycle. Individual results may vary. Always seek the advice of your physician or another qualified health provider with any questions regarding your menstrual health or fertility.
