Period Calculator
Period Calculator
How It Works
- Next Period: Calculated as LMP + cycle length. Period end is start date + period length.
- Cycle Day: Shows which day of your cycle you're on today and how many days remain.
- Ovulation: Estimated at cycle length − 14 days from LMP (standard formula).
- Fertile Window: Typically 5 days before to 1 day after ovulation.
- Irregular Cycles: Enter shortest and longest cycles to see prediction ranges.
Overview
Use ToolYard's Period Calculator to estimate when your next menstrual period will start based on your most recent period date and your average cycle length. The tool predicts your next period, future cycles, and current cycle day, and can optionally show your likely ovulation date and fertile window. It's ideal for tracking irregularities, planning around travel or events, or understanding your menstrual cycle better. All calculations run entirely in your browser for complete privacy—no data is stored or shared.
About
About Period Calculator
Predict your next menstrual period using your cycle length and last period date.
Features:
- Next period prediction
- Period end date calculation
- Cycle day tracking
- Cycle progress indicator
- Ovulation estimate
- Fertile window calculation
- Future period projections (3 months)
- Irregular cycle support
- Shortest/longest cycle ranges
- Copy summary
- Print results
- 100% private - no data stored
FAQ
How accurate is this Period Calculator?
It provides estimates based on your cycle length. Natural variation can shift dates by a few days. Tracking your actual periods over time improves accuracy.
Do I need a perfect 28-day cycle?
No—enter your actual cycle length. The tool works for cycles from 20–40 days.
Does this calculate ovulation?
Yes, if enabled. It uses the standard formula: cycle length − 14 days from your LMP.
Is my data saved?
No. All calculations run entirely in your browser and are not saved or transmitted.
Can irregular cycles still be predicted?
Yes. You can enter your shortest and longest cycles to get a prediction range instead of a single date.
What if my cycle is longer or shorter than average?
Enter your actual cycle length. The calculator adjusts all predictions based on your specific cycle.