Pebble

A planning aid, not medical advice.

Settings

Name Start End (optional)

No trial has tested shifting a progesterone start date around events specifically, but each assumption this planner relies on has published support:

The bleed is time-locked to the progestogen phase. In a UK multicentre study of 413 women on sequential HRT, most started bleeding around day 13 after starting the progestogen, roughly 1–2 days after finishing a 12-day course (Sturdee et al., Lancet 1994; see also Padwick et al., NEJM 1986).
The bleed day is predictable cycle to cycle, though onset varies between progestogen types and individuals, which is why this tool shades a “possible period” window rather than promising a date (BJOG 1995 dose-ranging study; regimen comparison, Maturitas 1994).
Moving a bleed by changing progestogen timing is established practice: norethisterone is routinely used to postpone periods, with randomised-trial support (NHS SPS guidance; norethindrone vs COC RCT).
Feeling worse during the progestogen days is recognised (“progestogen intolerance”, estimated 10–20% of women), and those symptoms track the phase (Newson Health overview).
Caveats: bleed timing does not indicate endometrial safety (J Clin Pathol 2001), and the evidence supports keeping at least 10–12 days of progestogen per cycle, which this tool never shortens. Discuss any change to your regimen, including gap length, with your prescriber.