The due date prediction is really dumb, just a random number between (I think) 325-350 days. Colts tend to "bake" a bit longer than fillies, mares can be up to a week early/overdue anyway, and if you add a maiden or older mare to the mix I think that early/late window extends to 3 weeks either way. So if the due date prediction is 325 days and it's a colt (so actually more like 350), plus the mare is 3 weeks late, you're looking at 46 days past due date.