How fast do young horse grow?
Eg
A filly with a May birthday stands at 14hh in March of her 2yr old year. She is predicted 15-16hh
Would she grow the extra hand between March and the first 2yr old races in April
Horses grow based on when they’ll hit their peak racing time.
Horses are also born at a varying % of their adult height (~57-63%, though premies can be bigger).
So your (hypothetical) foal is meant to be 16.1h when mature. She’s born in May at 60% of her adult height (16.1h = 65in x 0.60 = 39in = 9.3h). If she’s meant to be mature by September of her 3yo year, she’ll grow in proportion to that (so the 26 inches she’ll grow would be spread out over those 29 months).
Hope that helps clear things up. 
Thanks Shanthi, that’s a helpful tip for working out maturing points. Doesn’t quite answer the question though
Except it does, if your question is whether she’ll grow a full hand by April. 
She may or may not, depending on when she’s set to be mature (talent-wise) by then.
If she’s born January 2010 and is mature February 2012, she’ll be 16h by April race time.
If she’s born January 2010 and is mature May 2014, she won’t be 16h until she’s 4yo.
OK, thanks… I get it now. In other words “Watch this space so I know when she does best”
Yep, pretty much. There’s no “ding, your foal’s all done growing!” alert or anything, but by going off the estimated height, you should have a decent idea. Some people also track when their foals grow, which would give an indication of how often you should monitor height to see when they’re done (1in every month, 3 months, etc).
Just out of curiosity, when do they stop growing? Will they be fully grown by the end of their 2YO year or is there the possibility that they may still grow some more at 3YO?
I think Shanthi mentioned the answer above Lewis. Looks like they stop growing when mature, which can be any time from 2YO through 4YO (perhaps later?).
Oops, yes. I just noticed that. Thanks.
Horses can mature anywhere from 2-5 years. They’re guaranteed at least 1 year of mature time (before getting past their prime), but can have more than that (up to 4 years, I believe).