Period Calculator
Predict upcoming periods and ovulation dates
What is the Period Calculator?
The Period Calculator predicts when your next period will start — and if you want, the several after that. It also shows the expected end date of each cycle. This is genuinely useful for planning around events, travel, or just not getting caught off guard. CalciHub's version lets you see upcoming periods for up to 12 months based on your last period date and your typical cycle length. No account, no data stored, no subscription.
How Does It Work?
The calculation is built on the assumption that your cycle repeats at a consistent interval. Starting from your last period date, it adds your cycle length to predict each future start date. Your period duration tells it when each cycle ends.
Next Period Start = Last Period Date + Cycle Length
Period End = Next Period Start + Period Duration - 1
Subsequent periods repeat the pattern by adding cycle length each time.
Last Period Date = the first day of your most recent period
Cycle Length = average number of days between period start dates
Period Duration = average number of days your period lasts
How to Use CalciHub's Period Calculator
1. Enter the first day of your last period.
2. Input your average cycle length (usually 21-35 days).
3. Add your average period duration (typically 3-7 days).
4. Click Calculate to see your upcoming period schedule.
5. View results for the next several cycles laid out in a clear date format.
Tip: If your cycle varies from month to month, use the average of your last three to six cycles for a more reliable prediction.
A Quick Example
David's partner, Mia, wants to plan around an upcoming beach trip in July. Her last period started June 3rd. Her cycle is typically 28 days and lasts 5 days.
Inputs: Last Period = June 3, Cycle Length = 28 days, Period Duration = 5 days
Next Period: July 1 to July 5
Following Period: July 29 to August 2
Result: Mia's July 4th trip falls right at the start of her next cycle. She adjusts her travel plans to leave on July 6th instead, armed with a clear picture of her schedule well in advance.
Frequently Asked Questions
Cycle length naturally varies due to stress, illness, significant changes in weight or exercise, travel across time zones, or hormonal fluctuations. A prediction tool gives you a best estimate based on your average — it can't account for month-to-month biological variation.