Calculating the length of your menstrual cycle can be useful for a number of reasons, but it can be hard to do if you have irregular periods. Whether you want to identify when your fertile window is or you just want to know when your next period is likely to come, tracking your period can help. It may also be useful to know that even those who have regular periods can find it difficult to accurately calculate their cycle length. Fortunately, having even a rough estimate can be helpful.

Calculating your cycle with irregular periods

There are lots of factors that can cause period irregularity, some of which are more serious than others. However, it’s the symptoms of your irregular cycles that can have more impact on how difficult it is to predict your next period. You have an irregular period if the length of your cycle keeps changing significantly. This means that trying to calculate your cycle could be the thing that alerts you to the issue. It’s important to note that some variance in cycle length from month to month is to be expected, even in regular cycles.

One thing to take into consideration when calculating the length of your menstrual cycle is that outside factors can have an impact. External factors which can cause short term fluctuations in your average cycle length may include:

  • Contraceptive use
  • Lactation or breastfeeding
  • Pregnancy

Your periods may take a while to resume after you stop using hormonal contraceptives, after you have a baby or after you stop breastfeeding. They may also be irregular while your body adjusts. If you’ve recently experienced any of those events, it may cause your cycle calculations to be less accurate than desired. This can have an impact even if you usually have a regular period.


How to predict periods

If you’re interested in calculating your cycle length to help you predict periods, the first step is to make a record of your periods. You can do this with a paper calendar, use your phone’s calendar, or use a smartphone app to make it easier. Either way, it’s a good idea to track the length and heaviness of your periods in order to give yourself a better idea of what to expect. You might also find it helpful to track PMS symptoms, as patterns in PMS symptoms can give you an early warning signal that your period is going to start soon. These could include:

  • Abdominal bloating
  • Cramps
  • Nausea or headaches
  • Acne
  • Breast tenderness

When calculating your cycle length, it’s a good idea to use more than three recent periods. This helps to ensure that your results are as accurate as possible. Try not to use any periods which may have been affected by factors like recently stopping hormonal contraception, pregnancy or lactation. If possible, waiting until you have data on five or six periods is a good idea.

In order to calculate the length of a cycle, you need to know how many days have passed between the first day of one period and the first day of the next one. Calculate this figure for each of the cycles you’re using, then add them up to get a total number of days. Divide this total by the number of cycles you’ve included - for example, if you’ve included the data from five cycles, divide the total number of days by five. This will give you an average cycle length.

However, due to the irregular nature of some people’s cycles, it’s likely that this won’t be as accurate as you might hope. Nevertheless, tracking your cycle regularly can help you to spot patterns in your symptoms which may help you to notice when your next period is on its way. For example, some women experience PMS symptoms such as those we listed above in the days leading up to their period, which may help to give you an early warning.

Tracking other aspects of your cycle can also help you predict what your next period will be like. For example, keeping a record on the heaviness of your flow on a daily basis during your period can help you to spot patterns going forward. This may help you to predict the heaviness of your period next time, which can be helpful if you use pads or tampons and need to buy the correct absorbency.



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