Upvote:0
The I-94 is electronic. They also usually stamp the Admit Until date of the I-94 underneath the entry stamp for your convenience (so you don't have to look it up online), but sometimes they forget. In any case, it's the I-94 that's authoritative. (It's always a good idea to look up the I-94 anyway, because sometimes the dates don't match.)
Upvote:8
The immigration officer should have written/stamped the date on your passport, however if they didn't you can find the details on your I94 record on the CBP website at http://www.cbp.gov/i94