Cycle Progress
—
Key Dates This Cycle
Predict your next period with clarity
Menstrual cycles are part of everyday life, but they don’t always follow a perfect schedule. If you’re planning travel, noticing symptoms, tracking for contraception, or trying to conceive, it’s natural to want a dependable estimate of what’s next. This next period calculator is designed to help you predict your next period date, understand your cycle timing, and estimate your fertile window and ovulation day—without complicated math.
If your period is late, it’s also normal to feel anxious. A late or missed period can happen for many reasons, including stress, illness, changes in routine, or pregnancy. You can use this tool as a late period calculator or missed period calculator to get context on timing and decide what to do next. For a deeper late-period guide, visit our late period calculator.
What is a Next Period Calculator?
A period calculator (or menstrual cycle calculator) estimates the first day of your next period using two details: the first day of your last period and your usual cycle length. Many people also use it as a period tracking calculator to build consistency over time.
Because ovulation is often linked to the timing of your next period, the tool can also function as an ovulation calculator and fertile window calculator. These fertility estimates are especially helpful if you’re planning pregnancy or trying to avoid it. If you need help with timing for conception, you may also like the conception date calculator.
How menstrual cycles work (simple biology)
A cycle starts on Day 1, which is the first day of bleeding. After your period ends, your body prepares an egg. If an egg is released (ovulation), the lining of the uterus stays ready for a potential pregnancy. If pregnancy doesn’t happen, hormone levels drop and the lining sheds—this is your next period.
One key detail: the time between ovulation and your next period is often fairly consistent (commonly around two weeks), while the time before ovulation can vary more. That’s why a delay in ovulation usually leads to a later period. You can learn more about cycle basics from the NHS: Periods.
How to calculate your next period date
The simplest way to estimate your next period is: First day of last period + your average cycle length. For example, if your cycle is typically 28 days, the next period is often estimated 28 days after Day 1 of your last period. This is exactly what a period prediction calculator does.
If you’re not sure of your cycle length, use this approach as a cycle length calculator: track the first day of bleeding for 3–6 cycles and compute your average. The more data you have, the more useful the estimate.
Average cycle length vs irregular cycles
Some people have a steady pattern, while others have an irregular period calculator-type situation where cycles vary. Irregular cycles can be common in the first few years after your first period, after pregnancy, during breastfeeding, and during perimenopause. Certain medical conditions (like thyroid issues or PCOS) can also affect cycle regularity.
If your cycle changes by several days month-to-month, use a wider “expected range” instead of a single date. A calculator can still help you spot patterns—especially when you note major stress, travel, sleep changes, or illness.
Late period and missed period: what they can mean
A period is usually called “late” when it hasn’t arrived around your expected time based on your usual pattern. A “missed” period can mean you’re significantly past your expected window, or you skipped bleeding altogether.
Common reasons include stress, being sick, intense exercise, significant weight changes, travel and jet lag, stopping or starting hormonal birth control, and pregnancy. If you had recent unprotected sex or contraception failure, consider reading our guide on pregnancy test accuracy so you know when testing is most reliable.
Next period vs pregnancy: how to tell the difference
It can be hard to distinguish PMS from early pregnancy because symptoms may overlap (fatigue, mood changes, cramps, breast tenderness). The most reliable way to tell is a pregnancy test. If your test is negative but your period still doesn’t arrive, repeat in 48–72 hours or follow up with a clinician.
If you recently used emergency contraception, your timing may shift. Our emergency contraception calculator can help you interpret expected changes. If you’re trying to conceive, you may also want a pregnancy due date calculator after you confirm pregnancy.
Ovulation and fertile window overview
Ovulation is the release of an egg. Pregnancy is most likely when sperm is already present in the reproductive tract before ovulation, because sperm can survive for several days. That’s why your fertile window includes the days leading up to ovulation and the day of ovulation itself.
This tool estimates ovulation as roughly 14 days before your next expected period. That’s a helpful guideline, but it’s still an estimate. If you need precision, consider also tracking cervical mucus, ovulation tests, or basal body temperature. If you’re curious about what happens after conception, our implantation calculator calendar explains typical implantation timing.
Who should use this calculator?
- Anyone who wants a simple answer to “when is my next period” based on recent cycle history.
- People planning pregnancy who want an estimate of ovulation timing and fertile days.
- People avoiding pregnancy who want cycle context (note: it is not a guarantee of “safe days”).
- Anyone concerned about a late cycle who wants a clear estimate of how timing compares to their usual pattern.
If you’re using long-acting contraception (like the injection or implant), bleeding may be irregular or absent. In that case, a traditional menstrual calendar calculator may not reflect what’s happening hormonally. You may find these helpful: pregnancy after Depo calculator and pregnancy after implant calculator.
Accuracy, assumptions, and limitations
This period and ovulation calculator is most accurate when your cycles are fairly consistent. It assumes your next cycle will be similar to your average cycle length. If ovulation happens earlier or later than usual, your period will usually shift too.
Keep in mind:
- It’s an estimate, not a diagnosis or guarantee.
- Irregular cycles can produce wider prediction windows.
- Stress, illness, travel, postpartum changes, and medication can alter timing.
- Hormonal birth control can change bleeding patterns; “withdrawal bleeding” isn’t always a natural period.
If your cycle is very unpredictable, focus on tracking patterns and symptoms over time, not a single date. If you’re trying to prevent pregnancy, a “safe period calculator” approach can be risky—use reliable contraception and talk to a clinician about what fits your needs.
Medical disclaimer
FAQ
1) When is my next period?
Your next period is typically estimated by adding your average cycle length to the first day of your last period. If your cycle varies, the date can shift.
2) How do I calculate my cycle length?
Count from Day 1 of one period to Day 1 of the next. Track at least 3 cycles and use the average for better accuracy.
3) What if I don’t know my average cycle length?
Start with a common estimate (like 28 days) and adjust after tracking a few cycles. The calculator works best with your own average.
4) What is a normal menstrual cycle length?
Many people fall between 21 and 35 days. Some variation can be normal depending on age, postpartum status, and hormonal changes.
5) Why is my period late?
Late periods can happen due to stress, illness, travel, weight changes, intense exercise, hormonal shifts, thyroid issues, PCOS, breastfeeding, or pregnancy.
6) Can stress delay a period?
Yes. Stress can delay ovulation, and a later ovulation usually leads to a later period.
7) Can I be pregnant if my period is late?
Yes. Pregnancy is one common cause of a missed period, especially after unprotected sex. Consider a home test and follow guidance on timing.
8) When should I take a pregnancy test if I’m late?
Many tests are accurate from the day your period is expected. If negative but still no period, repeat in 48–72 hours or consult a clinician. See our pregnancy test accuracy guide.
9) What is ovulation?
Ovulation is when an ovary releases an egg. The egg survives about a day, but sperm can survive several days, which affects fertile timing.
10) What is the fertile window?
The fertile window includes the days leading up to ovulation and the day of ovulation. It’s the time when pregnancy is most likely from sex.
11) How does this ovulation calculator estimate ovulation?
It estimates ovulation as about 14 days before your next expected period. This is a guideline and can vary from person to person.
12) Can emergency contraception change my next period?
Yes. It can make your next bleed earlier or later. If your period is more than a week late, take a pregnancy test. You can also check our emergency contraception calculator.
13) Does birth control affect period predictions?
Yes. Hormonal methods can change bleeding patterns or stop bleeding. With some methods, bleeding may not reflect a natural ovulation-based cycle.
14) What if my periods are irregular?
Use your best average, but expect a wider range. Tracking 3–6 cycles and noting stress, travel, or illness can improve your understanding.
15) How late is “too late” for a period?
If your period is more than a week late, consider a pregnancy test if there’s any chance of pregnancy. If you miss 3 periods in a row (and are not pregnant), seek medical advice.
16) Can lifestyle changes affect my cycle?
Yes. Sleep disruption, intense training, travel, significant weight change, and illness can all affect ovulation timing and therefore period timing.
17) What should I do if my test is negative but my period is still missing?
Repeat the test in 48–72 hours, and consider contacting a clinician—especially if you have pain, unusual discharge, or heavy bleeding.
18) Is a “safe period calculator” reliable for avoiding pregnancy?
Calendar-based methods can be less reliable if cycles vary. If avoiding pregnancy is important to you, consider more dependable contraception options.
19) If I’m trying to conceive, what should I do next?
Use fertile window estimates as a guide and consider ovulation tracking. After pregnancy is confirmed, you can use the pregnancy due date calculator.
20) When should I see a doctor for missed periods?
Seek care if you miss 3 periods in a row (not pregnant), have severe pain, very heavy bleeding, fainting, or symptoms that worry you.