I didn't bank sperm until 5 months on HRT. Sperm analysis came back "low" in almost all areas but not subfertile in any. I didn't even bother stopping HRT, just stopped taking the T blockers for about 3 days (still took the estradiol). I'm also young though, I know it is certainly not unheard of to go sterile in a shorter period than that, although a lot of what I've read suggests that stopping HRT will probably remedy that before a year or so on HRT. In other words, as long as you aren't 40+ or had fertility problems pre HRT, you should probably be just fine.