Understanding your menstrual cycle

Getting to know your menstrual cycle can help you understand when you’re most likely to get pregnant during every month.

What is the menstrual cycle?

The menstrual cycle is what your body goes through to get ready for pregnancy. This cycle is the time from the first day of your period (first day of bleeding) up to the day before the start of your next period. 

Ovulation usually happens during the second half of the cycle. This is when an egg is released from one of your ovaries. To get pregnant, the egg needs to be fertilised by the sperm.

Ovulation doesn’t happen every month for every woman. There are some conditions that may interfere with ovulation, such as endometriosis and polycystic ovarian syndrome (PCOS). If you are not getting a monthly period and are trying to get pregnant, speak to your doctor.

How long is the menstrual cycle?

Women’s cycles can vary in length and from month to month, but the average is around 28 days. It’s normal to have regular cycles that are longer or shorter than this (from 21 to 41 days).

It doesn’t matter how long your cycle is, most women will ovulate around 10 to 16 days before the start of their next menstrual cycle.

Can I get pregnant at any time during my cycle?

Yes, but it’s unlikely you’ll get pregnant just before or just after your period. You are most fertile when you ovulate, so this is when you’re most likely to get pregnant. Understanding your cycle and knowing more about what is happening month during the month, can help you learn the best days to get pregnant.

Find out more about ovulation and fertility, including top tips for finding your fertility window. 

What if my cycle is irregular?

It can be more difficult to get pregnant if you have irregular periods because you may not ovulate regularly.

There are many possible causes of irregular periods, which may affect your fertility. For example:

Having irregular periods does not mean you won’t get pregnant and there are things you can do to boost your chances of success.

See your GP if your periods have stopped, you’re missing monthly periods or you have irregular periods and are struggling to get pregnant.

I’ve been using contraception. Will this affect my cycle?

This depends on what type of contraception you’ve been using. If you’ve been taking the pill, your period may be irregular when you first come off it, so try to give yourself up to 3 months for your natural menstrual cycle to get back to its ‘normal routine’.

The first period after stopping the pill is known as a ‘withdrawal bleed’. The next one after this is your first natural period.

The contraceptive injection can also affect your cycle. Your periods may change and become irregular, heavier, shorter, lighter or stop altogether. This can carry on for some months after you stop the injections.

If you use the contraceptive implant your fertility will return to normal as soon as it is taken out.

How soon can I get pregnant after coming off the pill?

You can get pregnant as soon as you come off the pill but if you’re trying to get pregnant, it’s a good idea to wait until you’ve had a natural period. This will give your body time to adjust and give you a chance to make sure you’re ready for pregnancy.

My menstrual cycle is still irregular. Has the pill affected my fertility?

It’s unlikely the pill has caused any fertility problems, but it can sometimes cover up problems you already have, such as missing periods or PCOS .This is because the pill prevents the ovaries from releasing an egg (ovulation), so although it’s normal to experience period-type bleeding on the pill, you don’t have a ‘real’ period.

Contact your GP if you’re still having irregular periods 3 months after stopping contraception.

Can I use my menstrual cycle to predict my due date?

Yes. You can work out how far along your pregnancy is (and therefore when the baby is due) by counting from the first day of your last period.

This can be confusing because you probably didn’t get pregnant until around 2 weeks later, after you ovulated. Even if do you know the date you got pregnant, this is counted as day 14 of your pregnancy (if your cycle is 28 days), not day 1.

Your pregnancy is calculated from your last menstrual period because every time you have a period this is the body’s way of getting ready for pregnancy. It also gives healthcare professionals a standard to follow because it’s very difficult to know exactly when the sperm fertilised the egg.

If your period is irregular or if you’ve recently been on the pill it will be harder to try and work out your due date.

The most accurate way to work out your due date is to have an ultrasound scan when you’re around 11 to 14 weeks pregnant. This is used to see how for along you are and check your baby’s development.

I’m pregnant but have some bleeding. Is this my period?

Implantation bleeding sometimes happens  pregnant women around the time theto period would have been due. Implantation is when the developing embryo plants itself in the wall of your womb. An implantation bleed is very light bleeding (spotting) that is usually pinkish and sometimes brown. Not everyone will have an implantation bleed.

It’s common to have light bleeding or ‘spotting’ without pain before 12 weeks. This isn’t often serious, but you should contact your doctor, midwife or Early Pregnancy Unit immediately to be checked, just in case.

Find out more about bleeding in pregnancy.


Clinical Knowledge Summaries (2016) Contraception – natural family planning https://cks.nice.org.uk/contraception-natural-family-planning#!topicSummary

NHS Choices. Periods and fertility in the menstrual cycle https://www.nhs.uk/conditions/periods/fertility-in-the-menstrual-cycle/ (Page last reviewed: 28/07/2016. Next review due: 28/07/2019)

NHS Choices. Irregular periods https://www.nhs.uk/conditions/irregular-periods/ (Page last reviewed: 09/04/2018. Next review due: 09/04/2021)

NHS Choices. Contraceptive injection https://www.nhs.uk/conditions/contraception/contraceptive-injection/ (Page last reviewed: 07/02/2018. Next review due: 07/02/2021)

NHS Choices. Contraceptive implant https://www.nhs.uk/conditions/contraception/contraceptive-implant/ (Page last reviewed: 22/01/2018. Next review due: 22/01/2021)

NHS Choices. When will my periods come back after I stop taking the pill?  https://www.nhs.uk/conditions/contraception/when-periods-after-stopping-pill/? (Page last reviewed: 17/07/2018. Next review due: 17/07/2021)



NHS Choices. Vaginal bleeding in pregnancy https://www.nhs.uk/conditions/pregnancy-and-baby/vaginal-bleeding-pregnant/ (Page last reviewed: 26/01/2018. Next review due: 26/01/2021)

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    Last reviewed on March 6th, 2019. Next review date March 6th, 2022.

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    Please note that these comments are monitored but not answered by Tommy’s. Please call your GP or maternity unit if you have concerns about your health or your baby’s health.
    • By DeAnn (not verified) on 5 Jul 2020 - 01:46

      Ive had my period on the 15th of last month n im suppose to get my periods on the 6th of every month ive been having sex sence then what could that mean im gaining weight

    • By Charity wanjala... (not verified) on 29 Jun 2020 - 17:59

      I saw my last drop on 29th May upto now haven't seen any signs of blood again , does it mean that am pregnant, just worried

    • By Favour (not verified) on 28 Jun 2020 - 21:11

      My last period was on the 27 of May and now we are in 28 of June can I still see my period

    • By mosun (not verified) on 25 Jun 2020 - 10:33

      I had sex four days to my menses and I had unprotected sex....it is 2months now...I haven't seen my menses...does this means I am pregnant?

    • By BEATRICE (not verified) on 23 Jun 2020 - 08:25

      am had sex on 18 july but on 21 july ihad my periods meaning am not pregnant

    • By Abubakar Fatima (not verified) on 21 Jun 2020 - 21:29

      I had sex the day before my period and now 8 days after my period, it came back. Am i sick or is it normal?

    • By Niki (not verified) on 19 Jun 2020 - 11:45

      My due date is not matching with last day of my periods Iwas on my periods 2 January 2020 but when I calculate from my due date it says my last period was on 28 December 2020

    • By Anonymous (not verified) on 16 Jun 2020 - 23:44

      I'm still breastfeeding my baby in two weeks time she will clock a year nine months.Have not been mensutrating since all this while not until last month May 11 that I see blood and I blessed for three days and the forth day was just a spot.I had sex during my ovulation period and after.Later I started having lower abdominal pains waist pains and cold.I didn't see my period thinking that I am pregnant but to my surprise I saw blood today 16th of June. I want to ask am I pregnant or not.

    • By Dacia dias (not verified) on 14 Jun 2020 - 22:33

      I want to know about pregancy n fertility n ovulation days to get pregnant waiting for ur reply

    • By Anonymous (not verified) on 14 Jun 2020 - 19:51

      From d day ave giving birth I didn't c my period I later seen it when my baby is 1year I seen it twice with is 11/⅝ I seen it again on 25/5 in did month I see it on 9/6 hope no problem

    • By vera (not verified) on 29 May 2020 - 20:48

      i have my last period on 3rd of may ended on 6th ... Am expecting it today but didn't seen it... Am confuse

    • By Cecilia (not verified) on 28 May 2020 - 07:19

      I started my period 4 of May and finish 7 and my circle is 28days, and have been having sex throughout, from what date will I go for pregnancy text

    • By Shakshi chib (not verified) on 24 May 2020 - 16:32

      I want to ask u something that my periods come on 5 may of dis year nd it's again come on 24 may it's normal ?

    • By Nacy (not verified) on 22 May 2020 - 15:31

      I last had my periods on the 16 of February had sex on the 23 n 24 of February, then again on the 3rd of March when could I have fallen pregnant on these dates?

    • By Rinku (not verified) on 17 May 2020 - 08:09

      M having problem regarding not stopping my periods since 12 days ..n i want to conceive ..so is it possible to conceive this time?

    • By Chole (not verified) on 15 May 2020 - 21:24

      So i had sexual intercourse on the 17th of September but got my period that month. I however had sexual intercourse again on the weekend on the 11th till 13th of October and never got my period. is it possible that i can be pregnant from the time i had sex in September?

    • By Victoria (not verified) on 15 May 2020 - 09:19

      Pls want to know if someone saw her period 15 of april when is the next dat

    • By Anonymous (not verified) on 13 May 2020 - 22:36

      Please I lastly saw my period on the 3rd of April up to now have not see my menses again does it mean I'm pregnant

    • By Sd (not verified) on 11 May 2020 - 13:52

      Good day,
      I had a miscarriage, bleeding on and off that started on the 30 of March and Continuously bleeding from the 3 of April and ended on the 10 of April. I had my first period on the 8 of May which only lasted for two days... please advise if this is normal.

      Thank you

    • By Kavita jain (not verified) on 9 May 2020 - 06:52

      I am 27 years old .have regular cycle of 28 days .I have uterien firbroid 5 .having size less than 1 cm .my period length is 2 days having medium bleeding.still am trying to conceive ..but not happening..wht should reasons for it.

    • By Kavita jain (not verified) on 9 May 2020 - 06:51

      I am 27 years old .have regular cycle of 28 days .I have uterien firbroid 5 .having size less than 1 cm .my period length is 2 days having medium bleeding.still am trying to conceive ..but not happening..wht should reasons for it.

    • By Edith osajie (not verified) on 8 May 2020 - 14:42

      My period is somehow, I don't understand help me

    • By Justine's (not verified) on 8 May 2020 - 07:19

      I thank you so much for this educative program to us women I have really appreciated and liked this thankyouuu

    • By Tebatso (not verified) on 30 Apr 2020 - 09:25

      Lastmonth I was having two period twice a moth,then this month my period started late which is yesterday, but was very bright red with littlebit cramps, can I be pregnant or what can be???

    • By Ogala Joy (not verified) on 29 Apr 2020 - 19:09

      I saw my menses on the 15th of this month and I'm having pain in my lower abdomen what could that be please give me answer soon please

    • By oluwatosin (not verified) on 20 Apr 2020 - 17:37

      i started my period on 16th april end 20th pls ma wish day can i have sex with my man dat i will get pregnant

    • By JV (not verified) on 17 Apr 2020 - 02:55

      I had sex on Jan 31 and got my period on Feb 12 but after that I didn't get my periods until now which means i skipped my periods for two straight months. Does this mean I'm pregnant ? Please suggest me..

    • By Stella (not verified) on 2 Apr 2020 - 23:05

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    • By Helen Gediah (not verified) on 28 May 2020 - 22:38

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