There are four distinct phases which make up the menstrual cycle. However, it can't be emphasised enough that a 28 day cycle is not the norm for everyone, there are huge variations from woman to woman. What matters is learning about your own cycle and determining what is normal for you !

1) Menses

This is the bleeding phase of your cycle. This generally lasts from 3 to 6 days and is simply your uterus shedding it's top lining and the unfertilised egg. The first day of full flow bleeding is known as 'Cycle Day 1' (or CD1 for short), and it's from here the rest of the cycle is counted.

2) The Proliferative Stage

Whats happening in the Ovaries :

Before you've even stopped bleeding, then brain is already sending signals out in preparation for the next ovulation. A hormone known as FSH (Follicle Stimulating Hormone) is sent out in pulses. This acts on the ovaries causing several follicles containing eggs to start enlarging and developing. Over time one will grow larger than the others.

Whats happening in the Uterus :

Another hormone, oestrogen is released. This hormone acts on the uterine lining, it encourages and helps the lining replace itself and also has an effect on cervical mucus making it very hostile at this time to sperm.

All of this happens gradually during the first week or two after menses with FSH stimulating the eggs and oestrogen replacing and rebuilding the uterine lining. Another point to be emphasised is that this phase is not a 'set' number of days long. Even in the most regular of women illness, stress and other factors can elongate this phase and delay ovulation taking place occasionally.

However, at some point in the cycle another two hormones will kick into action, FSH levels will fall and this will result in ovulation.

3) Ovulation

What's happening in the Ovaries :

LH (Luteinising Hormone) is now sent out. Sometimes known as a luteinising 'surge' because the levels rise very quickly to a peak and then fall. This hormone acts also on the follicles and at the same time changes cervical mucus so that it becomes much more sperm friendly. So with the rise of LH and the fall of FSH... The largest follicle in the ovary will rupture and an egg is released. It will be gently wafted into the fallopian tubes and so is ready for fertilisation

The egg (or Ovum) has a very limited life span of 12 - 48 hours at the most which is why for conception purposes intercourse should take place before ovulation so that sperm (with a life span of up to 5 days) are already in the fallopian tubes waiting when the egg is released.

Whats Happening in the Uterus :

Much as before, the lining is being replenished.

4) The Luteal Phase

This phase does have quite a rigid time frame. Again all women vary but generally this phase will last around 10 to 16 days and no more. In trying to conceive circles luteal phase days are counted as DPO (Days Past Ovulation).

What's happening in the ovaries :

LH production is abruptly halted now the egg has been released, also at this time, sperm friendly cervical mucus will dry up very quickly. The egg has been released but the follicle it came from still has work to do. This follicle is now called the 'Corpus Luteum' and once the egg has gone it immediately starts to produce progesterone hormones.

Whats happening in the Uterus :

While the oestrogen has rebuilt the lining, the effect of progesterone is to make it wonderfully spongy and thick. In other words, very receptive to any fertilised egg that may happen to come along and want to implant itself !

So, for up to 16 days after ovulation the body waits, the corpus luteum producing hormones geared towards thickening up and making the womb lining as cosy and as receptive as possible to any fertilised egg.
For reference, from fertilisation to implanation in the uterus... the whole process normally takes around 7 to 12 days.

So if no fertilised egg implants ? Well, the corpus luteum starts to degenerate and die and with the sudden drop in progesterone the uterine lining also starts breaking down. This will take us back ultimately to the first phase in the cycle with the uterus shedding it's lining and the egg.

The corpus luteum having a limited life span is why the luteal phase can never be very long. It is for this reason that women trying to conceive should be advised to have intercourse around 14 days before their estimated next period... not 14 days after the last one.

If we take for example a woman with a regular 35 day cycle. If this woman was advised to have intercourse counting up 14 days since her last period she would be completely missing ovulation every time by nearly a week ! This is because if her luteal phase is within the normal range she would not be ovulating until at least day 21 of her cycle NOT on day 14. If she knows her cycle well it's very easy for her to do the maths ie : 35 days - 14 luteal phase = ovulation around day 21 .

Similarly a woman with a short 25 day cycle should do similar 25 - 14 = ovulation around day 11.

With this in mind it's well worth if you a trying to conceive taking note of your menstrual dates over a few months to see what your average cycle length is. Doing the simple calculation above should give you a very good idea of timing.