Hi there
Firstly Rosie63 - I would say that the best time to start continuous combined HRT is immediately following your bleed when your womb lining is at its thinnest - so unless you've decided to start already, I would for example take the next month as normal, then stop for 3-4 days. Depending on when your bleed comes - when it's just past full flow then I would start the 100 mg every day. If you go straight from 200 mg to 100 mg then you may or may not bleed but the lining will have built up so I would say best to shed it and then go from there.
Re the days and months - you are both confusing between the calendar dates and days of the cycle!
Some gynaes - presumably yours Birdy - suggest (post-menopausal) women take their utrogestan on the first of every calendar month as it's easier to remember. This means a very slightly longer cycle ie 12 bleeds per year instead of 13 as it would be with a traditional 4 week (28 day) cycle.
The traditional HRT and menstrual cycle is 28 days and starts from Day 1 - which in the natural cycle is the first day of the bleed and on HRT is the first pill or patch of a new pack. This has nothing to do with the calendar date.
However if you are post-menopausal and starting HRT - you usually only have to worry about the cycle days once - since once you start the utrogestan - then you start it again for the next and each subsequent cycle 4 weeks from that date if you see what I mean? In practice I fiddle mine around a bit as I am on a longer cycle and work backwards to fit it in with whatever I am doing to avoid bleeding when I'm away, or prog withdrawal when I'm doing something important! I have to work it out months in advance sometimes!!!
Hope this helps and let us know how it goes Rosie63

Hurdity x