Period Calculator · Practical guide
How Many Days Until My Next Period?
Your countdown is simply your cycle length minus the number of days since your last period started.
At a glance
The Countdown Formula
The number of days until your next period is your cycle length minus the number of days since your last period began. If your last period started 22 days ago and you have a 28-day cycle, about 6 days remain. The calculator above does this for you: it predicts the next start date and shows the days remaining until it.
Interactive tool
Period Calculator
Enter your own values, then compare the result with the examples below.
Cycle Prediction
Countdown Table for a 28-Day Cycle
| Days Since Last Period Started | Days Until Next Period |
|---|---|
| 14 | 14 |
| 21 | 7 |
| 24 | 4 |
| 26 | 2 |
| 28 | Due today |
| 30 | 2 days past expected |
Shorter and Longer Cycles
The same arithmetic applies at any cycle length — only the total changes. On a 24-day cycle, day 21 means your period is due in about 3 days; on a 32-day cycle, day 21 leaves about 11 days. This is why knowing your personal average matters more than the default 28: a 4-day difference in cycle length moves every prediction by 4 days.
If the Countdown Reaches Zero
A negative countdown means your period is past due. A few days of variation is normal — stress, travel, and illness commonly delay ovulation and push the period back. If your period is more than a week late and pregnancy is possible, a home pregnancy test is the standard next step; persistent irregularity is worth discussing with a healthcare provider.
Frequently Asked Questions
How do I know what cycle day I am on?
The first day of your last period is cycle day 1. Count forward to today to find your current cycle day.
What if the countdown says my period is past due?
A few days late is common and often caused by stress, travel, or illness. If it is more than a week late and pregnancy is possible, consider a home pregnancy test.
Does the prediction work with irregular cycles?
Less reliably. The calculator assumes a steady cycle length, so the more your cycles vary, the wider the real window around the predicted date.
Why does cycle length matter so much?
Every prediction is built from it. A 24-day cycle and a 32-day cycle produce dates eight days apart from the same last period.