Period Calculator
Period · Ovulation · Fertile Window · Peak Day · Safe Days — 3-Month View
Enter the first day of your most recent period. Normal cycle: 21–45 days. All calculations happen on your device — no data is sent or stored.
How to Use a Period Calculator
A period calculator predicts your next period, ovulation date, fertile window, peak fertile day, and safe days — all based on your cycle length and last period date.
What are Period Days?
Period days are the days of active menstrual bleeding. A normal period lasts 2–7 days. This calculator highlights them in red so they are easy to identify.
What is the Fertile Window?
The fertile window is the 6-day span when pregnancy is possible — 5 days before ovulation and ovulation day itself. Shown in green, this is the window to focus on whether you are trying to conceive or avoid pregnancy.
What is the Peak Fertile Day?
The peak fertile day is the day just before ovulation when conception chances are highest. Cervical mucus is typically clear and stretchy (egg-white consistency) on this day.
What is Ovulation Day?
Ovulation is when your ovary releases a mature egg. It appears in pink on the calendar. The egg survives only 12–24 hours, making timing critical for conception.
What are Safe Days?
Safe days — shown in blue — are the days outside the fertile window when the natural risk of pregnancy is lower. However, no natural family planning method is 100% reliable, especially with irregular cycles.
How Accurate is This Calculator?
This calculator uses the standard luteal phase method (cycle length minus luteal phase days = ovulation day). Accuracy improves with regular cycles tracked over 3+ months. For best results, combine with ovulation predictor kits (OPKs) or basal body temperature (BBT) charting.
Frequently Asked Questions
Period Calculator
Period · Ovulation · Fertile Window · Peak Day · Safe Days — 3-Month View
Enter the first day of your most recent period. Normal cycle: 21–45 days. All calculations happen on your device — no data is sent or stored.
How to Use a Period Calculator
A period calculator predicts your next period, ovulation date, fertile window, peak fertile day, and safe days — all based on your cycle length and last period date.
What are Period Days?
Period days are the days of active menstrual bleeding. A normal period lasts 2–7 days. This calculator highlights them in red so they are easy to identify.
What is the Fertile Window?
The fertile window is the 6-day span when pregnancy is possible — 5 days before ovulation and ovulation day itself. Shown in green, this is the window to focus on whether you are trying to conceive or avoid pregnancy.
What is the Peak Fertile Day?
The peak fertile day is the day just before ovulation when conception chances are highest. Cervical mucus is typically clear and stretchy (egg-white consistency) on this day.
What is Ovulation Day?
Ovulation is when your ovary releases a mature egg. It appears in pink on the calendar. The egg survives only 12–24 hours, making timing critical for conception.
What are Safe Days?
Safe days — shown in blue — are the days outside the fertile window when the natural risk of pregnancy is lower. However, no natural family planning method is 100% reliable, especially with irregular cycles.
How Accurate is This Calculator?
This calculator uses the standard luteal phase method (cycle length minus luteal phase days = ovulation day). Accuracy improves with regular cycles tracked over 3+ months. For best results, combine with ovulation predictor kits (OPKs) or basal body temperature (BBT) charting.