Period calculator: when is my next period?
Next period: Friday, November 13
That’s in 18 days.
- Fri, Nov 13 – Tue, Nov 17
- Fri, Dec 11 – Tue, Dec 15
- Fri, Jan 8 – Tue, Jan 12
- Fri, Feb 5 – Tue, Feb 9
- Fri, Mar 5 – Tue, Mar 9
- Fri, Apr 2 – Tue, Apr 6
🔒 Calculated in your browser. Nothing you type is sent or stored. Estimates only: cycles vary.
Add your usual cycle length to the first day of your last period: that's the day your next period is likely to start. If your last period began on 3 March and your cycles are 29 days long, expect the next one around 1 April. The calculator above does it for the next six cycles.
How the period calculator works
Your cycle starts on the first day of real bleeding (not spotting) and ends the day before your next period. The calculator takes that first day, adds your usual cycle length, and repeats it to show your next six periods. It also colours the current cycle by phase, so you can see roughly where you are today.
- Pick the first day of your most recent period.
- Set your usual cycle length. If you don't know it, start with 28 and use our cycle length calculator once you have a few dates.
- Set how many days you usually bleed (most people bleed for 3 to 7 days).
- Read your next period date, the following five, and today's phase.
Everything is calculated in your browser. Nothing you type is sent to us or saved anywhere.
How accurate is a period calculator?
A calculator is only as good as the cycle length you give it. Very few people have the same cycle every month: a normal cycle can be anywhere from 21 to 35 days in adults, and it's normal for it to move by a few days from one month to the next. Teens and people approaching menopause often vary even more.
That's why it helps to treat the date as a window, not a promise. If your cycles swing between 27 and 31 days, your period could reasonably start any day across those five days.
| If your cycles are… | Your next period is likely… |
|---|---|
| Regular (within 2 to 3 days of each other) | within a day or two of the predicted date |
| A bit variable (up to 7 days apart) | anywhere in a week-long window |
| Irregular (more than 7 to 9 days apart) | hard to pin down from averages alone; tracking symptoms helps |
What can make your period early or late
Most of the change in cycle length comes from when you ovulate. The time from ovulation to your period (the luteal phase) stays fairly steady at about 12 to 14 days, but the first half of the cycle can stretch or shrink. Things that commonly delay ovulation, and so your period, include:
- Stress, travel, illness or a big change in sleep
- Intense exercise or eating much less than usual
- Coming off hormonal contraception
- Breastfeeding, PCOS, thyroid conditions and perimenopause
- Pregnancy: if your period is late and you could be pregnant, take a test
If your period is more than a week late and a test is negative, our guide to why your period is late walks through the usual reasons.
Make the prediction smarter over time
A one-off calculation uses one number. A tracker learns from every cycle you log: your real average, how much you usually vary, and when your period tends to arrive. Lulu goes one step further and learns how you usually feel in each phase, so you can see the PMS days coming as well as the period itself.
When to talk to a doctor
See a doctor if your cycles are regularly shorter than 21 days or longer than 35, if your period stops for 3 months or more, if you bleed between periods or after sex, or if bleeding is very heavy (soaking a pad or tampon every hour or two).
Frequently asked questions
How do I calculate my next period?
Add your average cycle length to the first day of your last period. For example, a period that started on 10 June with a 30-day cycle points to 10 July for the next one.
Is the first day of spotting day 1 of my cycle?
No. Day 1 is the first day of real flow that needs a pad, tampon, cup or period underwear. Light spotting before that belongs to the previous cycle.
Can a period calculator tell me if I'm pregnant?
No. A late period can be a sign of pregnancy, but only a pregnancy test can tell you. Our pregnancy test calculator shows when a test is most reliable.
What if my cycles are irregular?
Use your average, but expect a wider window. Logging a few months of periods shows your real range, and a tracker like Lulu adapts its predictions to it instead of assuming 28 days.
Sources
- NHS: Periods
- ACOG: Menstruation in Girls and Adolescents: Using the Menstrual Cycle as a Vital Sign
- Bull JR et al. Real-world menstrual cycle characteristics of more than 600,000 menstrual cycles. npj Digital Medicine (2019)
This page is for information only and isn’t medical advice. If something worries you, please talk to a doctor.
Keep reading
Ovulation calculator: when do I ovulate?Free ovulation calculator: enter your last period and cycle length to see your likely ovulation day for the next 4 cycles. Private, instant, estimates only.
What phase of my cycle am I in? Free phase finderWhat phase of my cycle am I in? Enter your last period to see your cycle day, today's phase and how people often feel in it. Private and instant.How long is a normal menstrual cycle?How long is a normal menstrual cycle? Anywhere from 21 to 35 days in adults. What's average, how much variation is fine, and when to see a doctor.
Why is my period late? 10 common reasonsWhy is my period late if you're not pregnant? Stress, late ovulation, weight change, PCOS, perimenopause and more, plus when a late period needs a doctor.The 4 phases of the menstrual cycle, in colorThe 4 phases of the menstrual cycle explained simply: what your hormones do in each, how long each lasts, and how mood and energy usually change.