Next Period Calculator
Use this next period calculator to estimate when your next period may start and plan ahead using your usual cycle length.
Ready when you are
Select your last period date above to instantly unlock your personalized cycle predictions.
April 16
In 16 days
16 Days
Based on cycle averages
Fertile Window
Day 13 of cycle
Mar 28 - 3
Highest chance of conception
Future Forecast
This forecast works best for fairly regular cycles.
Event Planner
Planning a trip or event? Enter the date to check your estimated cycle phase.
Cycle Map
Tap the colored segments to see specific dates.
Support & Planning
What this estimate is best for
Having a reliable forecast of your next cycle allows you to prepare physically and mentally for the month ahead.
Check if your period might overlap with a vacation or important date.
Know exactly when to stock up on tampons, pads, or pain relief.
Understand if symptoms like bloating mean your period is actively arriving.
Look months ahead to map out your general biological rhythm.
Understanding Biology
What can shift your next period date
Even with a perfectly regular history, your expected date is an estimate. These common factors can easily shift your timeline by a few days.
Mental and physical stress can temporarily delay ovulation.
Time zone changes and poor sleep disrupt your internal rhythm.
Being sick forces your body to prioritize recovery over reproduction.
A shift of 2 to 3 days is completely normal biological behavior.
How it works
How this next period calculator works
This tool adds your usual cycle length to the first day of your last period to estimate when your next period may start. It also uses that estimate to show your likely fertile window and forecast the next few cycle dates.
Limits
What this estimate can and cannot do
- • Useful for planning around your next expected period date.
- • Helpful for seeing when your next cycle may begin.
- • Not designed to guarantee one exact day.
- • Less useful when cycles are highly irregular.
Use this page if...
Your cycle is fairly regular and usually falls within a few days of your average cycle length month to month.
Use the irregular calculator if...
Your dates swing a lot from month to month. A broader probability range is more realistic than a single date.
Go to Irregular Calculator →FAQ
Next period questions
1How does the next period calculator work?+
It uses a straightforward calendar-based formula: adding your average cycle length to the first day of your last period. This estimates when your next period may start and gives supportive fertile-window and ovulation timing guidance.
2How many days can a next period estimate shift and still be normal?+
A shift of 2 to 3 days from your expected date is considered completely normal biological variation. Human bodies are not clocks, and slight changes are very common.
3Is this calculator useful if my cycle changes a little month to month?+
Yes. Most people have variations of a few days. Using your most common cycle length will give you the best baseline estimate for planning.
4Why does my predicted next period sometimes move?+
Hormones control your cycle, and they are highly sensitive to your environment. A delayed ovulation automatically delays your next period start date.
5Can travel or stress shift the result?+
Yes. Significant changes to your routine, time-zone travel, illness, or high stress can delay ovulation, which naturally pushes your period back.
6Can it tell me the exact day my period will start?+
It gives a useful estimate based on your average cycle length, but human biology naturally fluctuates. A shift of 2 to 3 days from your expected date can still happen because of stress, travel, illness, or normal hormonal variation.
7Is my tracking data private?+
Yes, 100% private. We use local browser storage on your device so the calculator remembers your cycle length for your next visit without ever sending your health data to a server. There are no accounts and no sign-ups.
8How does the future cycle forecast work?+
By rolling your average cycle length forward, the calculator projects your likely period dates for the next three months. This is especially useful for planning vacations, weddings, or athletic events.
9Can I use this if my cycle is highly irregular?+
If your cycle length changes by more than 7 days from month to month, an exact date calculator may cause unnecessary anxiety. We highly recommend using our dedicated Irregular Period Calculator instead, which maps out a broader, more realistic probability window.
Next step
Use a related tool or guide
If your main question is about late timing, cycle length, or why dates move month to month, these are the best next pages.