How do I predict my next period?

Add your average cycle length to the first day of your last period. For example, if your last period started March 1 and your cycle is 28 days, the next period is expected March 29.

What is a normal menstrual cycle length?

A normal cycle is between 21 and 35 days. The average is 28 days. Cycle length can vary naturally by a few days month to month.

When is my fertile window?

Ovulation typically occurs 14 days before your next period. The fertile window is the 5 days before ovulation plus the ovulation day — a 6-day window when pregnancy is possible.

What is the luteal phase?

The luteal phase is the time between ovulation and your next period. It is typically 12-16 days (average 14 days) and is relatively consistent across cycles.

When should I take a pregnancy test?

Take a pregnancy test on the first day of a missed period or after your late period alert date passes. hCG levels are high enough for detection from this point onward.

Period Calculator

Predict your next period date, fertile window, and ovulation day. Track cycle regularity and plan ahead with a 6-month projection.

Last Period Start Year

Last Period Start Month (1-12)

Last Period Start Day (1-31)

Average Cycle Length

days

Period Duration

days

Next Period Date

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2nd Period —

3rd Period —

Fertile Window —

Estimated Ovulation —

Extended More scenarios, charts & detailed breakdown ▾

Last Period Year

Last Period Month (1-12)

Last Period Day (1-31)

Cycle Length

days

Period Duration

days

Next Period

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2nd Period —

3rd Period —

Ovulation —

Fertile Window —

Professional Full parameters & maximum detail ▾

Last Period Year

Last Period Month (1-12)

Last Period Day (1-31)

Average Cycle Length

days

Period Duration

days

Luteal Phase Length

days

Typical Cycle Variation

days

Late Period Alert Threshold

days

6-Month Calendar Projection

Next Period (expected) —

2nd Period —

3rd Period —

4th Period —

5th Period —

6th Period —

Fertility & Ovulation

Ovulation (next cycle) —

Fertile Window —

Cycle Analysis

Late Period Alert Date —

Cycle Assessment —

How to Use This Calculator

Enter the date of your last period (year, month, day as separate fields).
Set your average cycle length (default 28 days) and period duration (default 5 days).
The calculator predicts your next 3 period dates, ovulation day, and fertile window.

Formula

Next Period = Last Period Start + Cycle Length
Ovulation = Next Period − 14 days
Fertile Window = Ovulation − 5 days through Ovulation + 1 day

Example

Example: Last period March 1, cycle 28 days. Next period: March 29. Ovulation: March 15. Fertile window: March 10–16.

Frequently Asked Questions

Add your average cycle length to the first day of your last period. For example, if your last period started March 1 and your cycle is 28 days, the next period is expected March 29.
A normal cycle is between 21 and 35 days. The average is 28 days. Cycle length can vary naturally by a few days month to month.
Ovulation typically occurs 14 days before your next period. The fertile window is the 5 days before ovulation plus the ovulation day — a 6-day window when pregnancy is possible.
The luteal phase is the time between ovulation and your next period. It is typically 12-16 days (average 14 days) and is relatively consistent across cycles.
Take a pregnancy test on the first day of a missed period or after your late period alert date passes. hCG levels are high enough for detection from this point onward.

Related Calculators

Sources & References (5) ▾