Hi there debsmeno

Cassie has given you the short answer which is easy to follow when you know how....
Here is the long answer:
There always seems to be confusion about when to take Utrogestan - understandably!
Firstly it depends on whether you are peri or post-menopausal and the length of your normal menstrual cycle – ie whether you are trying to fit in with the average 28 day cycle?
The licensed dose of Utrogestan for cyclical HRT is 200 mg for 12 days per 28 day cycle days 15-26.
To do this - if you are in early peri-menopause: for a 28 day cycle – say you are starting HRT (Utrogestan and Estrogel) for the first time : Day 1 is the first day of your (normal) bleed. Start the oestrogel Day 1. When you get to Day 15 start the Utrogestan. Take it for the last time on Day 26 (ie 12 days). Day 27 go back to the oestrogel only and on Day 28. Ideally you would start your bleed on Day 1 again – but in practice it may not happen. However the usual advice is to stay with the cycle and keep with the course of Utrogestan and more to the point you just restart counting Day 1 whether or not you have bled. You just carry on taking the oestrogel until Day 15 again. Easy to set up on your calendar as it will be the same day of the week, but 4 weeks after your first Day 1 if you see what I mean!
Also if you are having irregular periods then you might be waiting forever for your next period ie Day 1 so the usual advice is to start anytime. You might then be out of sync with your own cycle so sometimes you can readjust by starting to count again on your bleed (to give a new Day 1) if you end up getting periods substantially at the wrong time.
Once your periods become few and far between or you are post-menopausal then your natural cycle becomes irrelevant or nearly so. Then you can in effect choose your cycle as Cassie does – and keep with the 28 day cycle (which keeps your bleeds/progesterone withdrawal symptoms to the same days of the week if you respond the same each month) or stretch the cycle a bit to 12 cycles per annum rather than 13 and go with the calendar month ie the first of every month to start your Utrogestan (or whatever day you choose eg 15th !).
Some of us stretch the cycle even further (with doc's approval) due to lack of bleed on the shorter cycles – and this minimises progesterone exposure.
Even if you are peri-menopausal it might work out OK as Cassie does it ie take it every calendar month on the same date?
Well I did say it was long

Hope it helps though!
Hurdity x