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.
Anywhere from 21 to 35 days is considered within the normal range for adults. Cycles shorter than 21 days or longer than 35 days on a regular basis are worth mentioning to a doctor. Teenagers and people in perimenopause often have more variability, which is expected.
This calculator is not a contraceptive tool and should not be used as one. The rhythm method based on calendar tracking has a relatively high failure rate compared to other contraception options. If avoiding pregnancy is the goal, speak with a healthcare provider about effective options.
CalciHub's Period Calculator can project up to 12 months ahead. The further out the prediction, the less precise it becomes — small cycle variations accumulate over time. Use it for general planning, not day-to-day.
Yes, fully free. No personal data is stored, and no account is required.
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