How very timely that you should ask.
May I present the M2F 'bottom surgeries' carried out by NHS England since 2013. a total of 1445 in 5 years. Of course some of these may include the reddit special where the penis remains, but let's not dwell on that.
There are some other published figures from a different FOI that suggest various 'completed consultant episodes' for 'sexual transformations' which includes a whole lot of different operative procedure codes and are probably over-counting, since they may not be strictly all genital surgery.
By my estimates I'd suggest ~1200 operations between 2004 and 2013. A total of ~2641 m2f bottom surgeries carried out in England in the 14 years since the GRA.
so. Make of that what you will. How many male people identify as transwomen in England currently?
300k? then >99% of them keep their penis.
200k? then 98.7% keep their penis.
100k? then 97.4% keep their penis
Perhaps we should include an allowance for the operations that happen in Thailand or privately?
What do we think? an extra 25%?
In that case, the most generous estimate is that with 3300 operations, on the smallest population estimate of 100,000 transwomen, 96.7% keep their penis.
Feel free to correct population estimates, or inflate those extra operations to derive percentages. This data is only for England.