Text with personality
Turn plain words into tiny, raised, mirrored and symbol text you can paste anywhere.
Browse fancy textQuick calculators
Percentages, money, grades, math, age, sleep and time tools.
Browse all calculatorsHealth calculators
Calories, macros, body, training, pregnancy and cycle tools.
Browse all calculatorsNumber and code tools
Binary, hex, Roman numerals, Base64, URL encoding and passwords, all in your browser.
Browse all calculatorsEnter the first day of your last period, your cycle length and period length to see predicted dates for the next 12 periods, today’s cycle day and a range if your cycles vary. An estimate only, not contraception.
Estimates only. Cycles vary from month to month, so these dates are predictions worked out from the numbers you typed, for cycles of typical length. They are not a method of contraception and not a way to find safe days: ovulation can fall on a different day, so pregnancy is possible outside the estimate. Only a doctor, midwife or an ultrasound dating scan can confirm pregnancy dates. A late or missed period, or periods that are very heavy or painful, are reasons to talk to a doctor.
This is a general estimate for educational use. It is not medical advice, a diagnosis or a treatment plan. Talk to a doctor or other qualified professional before you make any decision about contraception, pregnancy or health care.
Cycle length is counted from the first day of one period to the first day of the next, from 21 to 45 days. The NHS gives 21 to 35 days for regular cycles and womenshealth.gov gives 24 to 38 days.
Each row repeats the same cycle length. Scroll sideways for every column.
| Period | Starts | Ends | Cycle (days) | Ovulation (est.) | If cycles vary |
|---|
Private by design. Everything runs in your browser and is never uploaded.
A period calculator predicts your next period by adding your cycle length to the first day of your last period, then repeating that for each later cycle. This one lists the next 12 periods with start and end dates, shows today as a cycle day, and adds an estimated ovulation day. The dates are estimates, because cycles vary.
Cycle length is counted from the first day of one period to the first day of the next. Results update as you type, and a cycle variation setting shows how the next start could shift when your cycles are not all the same length. For the full fertile window use the Ovulation Calculator, which covers it in detail. To date a pregnancy use the Pregnancy Calculator or the Due Date Calculator.
| Cycle length | Next period starts | Next period ends | Ovulation estimate | 12th period starts |
|---|---|---|---|---|
| 24 days | Thu, Nov 26 | Mon, Nov 30 | Thu, Nov 12 (day 11) | Aug 17, 2027 |
| 26 days | Sat, Nov 28 | Wed, Dec 2 | Sat, Nov 14 (day 13) | Sep 10, 2027 |
| 28 days | Mon, Nov 30 | Fri, Dec 4 | Mon, Nov 16 (day 15) | Oct 4, 2027 |
| 30 days | Wed, Dec 2 | Sun, Dec 6 | Wed, Nov 18 (day 17) | Oct 28, 2027 |
| 32 days | Fri, Dec 4 | Tue, Dec 8 | Fri, Nov 20 (day 19) | Nov 21, 2027 |
| 35 days | Mon, Dec 7 | Fri, Dec 11 | Mon, Nov 23 (day 22) | Dec 27, 2027 |
The first answer is already on screen. Change any field and every date updates at once, with no Calculate button.
Choose the date your last period began, or type it as YYYY-MM-DD or Nov 2, 2026. The page starts with a date 10 days ago so an answer shows straight away.
Cycle length runs from 21 to 45 days and starts at 28. Period length runs from 2 to 10 days and starts at 5. Both are counted with the first day as day 1.
Choose how many days your cycle can run shorter or longer, from 0 to 10. The result then shows a window for the next start instead of a single day.
Read the table of the next 12 periods, open the working, copy the result, share a link with the same settings or save the dates as a calendar file.
The defaults, the accepted ranges and the notes on this page come from these figures. Sources do not agree on one range, so the page shows both and does not label any length.
| Source | What it says | Used here for |
|---|---|---|
| NHS, Periods | Most women have a period around every 28 days, and frequency can range from every 21 to every 35 days. A period can last 2 to 7 days and usually lasts about 5. | Defaults of 28 and 5 days; notes outside 21 to 35 days and above 7 days. |
| NHS, Fertility in the menstrual cycle | In most women ovulation happens around 10 to 16 days before the next period. It is difficult to pinpoint exactly when it happens. | Ovulation estimate placed 14 days before the next period. |
| womenshealth.gov, Your menstrual cycle | The cycle is counted from the first day of one period to the first day of the next. A typical cycle is 28 days, and a range of 24 to 38 days is given. The time from ovulation to the next period can be anywhere from about 7 to 19 days. Cycles can differ from month to month. | How the cycle is counted; the second range in the notes; the case for an estimate only. |
| Bull and others, npj Digital Medicine, 2019 | In 612,613 ovulatory cycles from app users the mean cycle length was 29.3 days (standard deviation 5.2). The cycle lengths of one person varied by 2.6 days on average (standard deviation). The authors state that ovulation on day 14 of every cycle is not correct. | The idea that cycles vary, and the reason the variation setting exists. |
A period calculator repeats one cycle length, but a real cycle changes from month to month. A small error in the cycle length you typed is added again for every later period. If your true average is 1 day away from the number you typed, the 12th predicted period is 12 days away from the real one.
The cycle variation setting shows the same effect as a window. With a 28-day cycle, a variation of 3 days and a last period on Nov 2, 2026, the next start falls between Nov 27 and Dec 3, 2026, and the 6th period could start anywhere from Apr 1 to May 7. From period 5 onward the window is wider than a whole cycle, so the table marks those rows. The window assumes every cycle is off in the same direction, which is the widest case.
Enter the real start date after each period. That resets every date and keeps the prediction close to today.
| Average is off by | Period 1 | Period 3 | Period 6 | Period 12 |
|---|---|---|---|---|
| 1 day | 1 day | 3 days | 6 days | 12 days |
| 2 days | 2 days | 6 days | 12 days | 24 days |
| 3 days | 3 days | 9 days | 18 days | 36 days |
Many pages ask for a date and a cycle length and show a short list. These are the differences that matter when you want to understand the dates.
| Feature | Basic period calculator | This calculator |
|---|---|---|
| Periods listed | Often 3 to 6 | The next 12, with start, end and cycle length |
| Cycles that vary | One date per period | A window for the next start, widening with each cycle, set by you |
| Today | Not shown | Cycle day today, and what to enter if the predicted date has passed |
| Ovulation | Often a fertile window with little warning | One estimated day per cycle, plus a link to the Ovulation Calculator for the window |
| Working | Answer only | Every step of the date maths, and the figures behind the defaults |
| Safety wording | Often a footer disclaimer | A not-contraception and estimates-only note beside the result |
| Sharing | Rare | Copy the result, share a link, or save a calendar file |
See the predicted start and end dates before a trip, an exam or an event. The window shows how far the start could move.
Compare each predicted date with the day a period really starts. The gap tells you how far your own cycles vary from the number you typed.
Save the upcoming predicted periods as a calendar file and open it in your phone or computer calendar. The file is made on your device.
Change the variation from 0 to 10 days and watch the window for the next start grow. It shows why one date is a weak guide when cycles vary.
Share a link that opens with the same settings. The dates are in the link, so send it only to someone you choose.
Use the Ovulation Calculator for a fertile window, the Pregnancy Conception Calculator to estimate a conception date, or the age calculator for dates of birth.
Every date is a whole calendar day, so time zones and clock changes cannot move it. Each step is in the working under the table.
Estimates only, not contraception. Cycles vary, so these dates are predictions for cycles of typical length. They are not a method of contraception and not a way to find safe days. A late or missed period, or periods that are very heavy or painful, are reasons to talk to a doctor.
The first day of the last period plus the cycle length. Period 2 adds the cycle length twice, period 3 three times, up to period 12.
The start date plus the period length minus 1, because the first day of bleeding counts as day 1.
Period k falls between the last start plus k times (cycle minus variation) and k times (cycle plus variation). It is the widest case, where every cycle runs short or long.
The start of the next period minus 14 days, so day 15 of a 28-day cycle. The NHS places ovulation 10 to 16 days before the next period. The Ovulation Calculator lets you change that number and shows the fertile window.
Today minus the first day of the last period, plus 1. If the predicted start has already passed, the page says so instead of counting on silently.
This page cannot say why a period is late. That is a question for a doctor or nurse. If a pregnancy is confirmed, the Pregnancy Calculator shows weeks and key dates.
It repeats one cycle length, so it cannot follow the changes real cycles make. The 2019 study of more than 600,000 cycles found that the cycle lengths of one person varied by 2.6 days on average.
The ovulation day is an estimate and cannot be used to find safe days. The NHS says it is difficult to pinpoint exactly when ovulation happens, and that pregnancy soon after a period is possible, although not very likely, if ovulation is early or the cycle is short.
It does not diagnose anything or say whether a cycle needs attention. womenshealth.gov lists when to talk to a doctor or nurse, and the NHS periods page says where to get a change in your periods checked.
Every figure in the reference table and the notes comes from the four pages below, which were opened for this page. The date maths (adding days to a calendar date) is plain arithmetic and needs no source.
Short answers about cycle length, the dates and the limits of this calculator.
Add your cycle length to the first day of your last period. With a last period starting Nov 2, 2026 and a 28-day cycle, the next period is predicted for Mon, Nov 30, 2026. Add the cycle length again for each period after that. The calculator does this for the next 12 periods and shows the working.
From the first day of one period to the first day of the next, so the first day of bleeding is day 1. womenshealth.gov counts the cycle the same way. The length is not the number of days the bleeding lasts.
Published figures differ. The NHS says most women have a period around every 28 days and lists regular cycles of 21 to 35 days. womenshealth.gov gives a typical cycle of 28 days and a range of 24 to 38 days. This calculator accepts 21 to 45 days and adds a note when a length falls outside either range.
The NHS says a period can last between 2 and 7 days and usually lasts about 5 days. This calculator accepts 2 to 10 days, starts at 5, and adds a note above 7 days. The end date it shows counts the first day as day 1.
Use the Cycle variation setting. It is the number of days your cycle can run shorter or longer than the length you typed. The result then shows a window for the next start: with a 28-day cycle and a variation of 3 days, the next start falls between 25 and 31 days after the last start. One large app-based study found that the cycle lengths of one person varied by about 2.6 days on average (standard deviation).
Each cycle can be off in the same direction, so the possible error adds up. With a 3-day variation the window is 7 days wide for the next period, 13 days for the one after and 19 days for the third. From period 5 onward the window is wider than a whole 28-day cycle, and the table marks those rows as wider than a cycle.
It is an estimate. It repeats one cycle length, while real cycles change from month to month, and a small error grows with each cycle: a cycle length that is 1 day off moves the 12th predicted period by 12 days. Dates for the next period are more useful than dates a year ahead, and entering the real start date after each period resets everything.
It is placed 14 days before the next period starts. The NHS says ovulation happens around 10 to 16 days before the next period in most women, and womenshealth.gov says the gap can be anywhere from about 7 to 19 days. It is a secondary estimate on this page. The Ovulation Calculator lets you change the luteal phase and shows the full fertile window.
No. It is not a method of contraception and not a way to find safe days. The ovulation day is an estimate, cycles vary, and pregnancy is possible outside the dates shown. A doctor, nurse or pharmacist can explain contraception options.
This page cannot say why a period is late. A late or missed period is a reason to talk to a doctor or nurse. The NHS and womenshealth.gov both list missed periods among the times to do so. If a pregnancy is confirmed, the Pregnancy Calculator counts weeks from the last period.
womenshealth.gov lists cycles longer than 38 days or shorter than 24 days, no period for 90 days when not pregnant or breastfeeding, bleeding that soaks through a pad or tampon every one to two hours, and period pain or bleeding that causes missed school or work. This page only points to that list and does not assess anyone.
No. The calculation runs in your browser and nothing is sent to a server. The dates appear in the page address only after you change a value or tap Share link, so anyone who gets that link can see them. The calendar file is created on your device.