"by date X" exact meaning

[ringo-ring]

So I lost patience this morning and emailed my program asking whether they're going to take me or not, and surprise, got a reply that I will get a reply from them "by April 15". But I have trouble translating this from English. Does this phrase mean I'll get a reply on April 15 exactly or near to this date, or anytime before? Native speakers - Please help!

[Trin]

There's another option you didn't include in your poll. "By April 15" carries with it the implication that it may be *close* to April 15. So I wouldn't say "could happen any time, starting now", I'd say, "will arrive on or before April 15, but probably close to that date." Does that make sense? Honestly, I tend to look at when whatever school has notified in the past, and use that as a gauge of about when they will notify this year.

It's also possible that the school has rolling admissions, so they notify when they've made a decision, but no later than April 15.