Misunderstanding (inclusive/exclusive)

Someone wrote to me, in Japanese, 「8/21までお休み」which, in my brain I translated 「まで」to mean "until" - on vaction until 8/21. But I found out, the hard way, that it's not an exact translation. In English "until" is kind of ambiguous, but usually when someone says "I'll be on vacation until the 21st" it means that on the 21st they will stop being on vacation and will be available. But 「まで」I found out (the hard way) means the 21st is included in the vacation period. Another example is "we will be out of coffee until the 21st" which I take to mean we'll have coffee on the 21st.
So when you're speaking to a Japanese learner be aware that there are many holes and gaps in their understanding. I'm made painfully aware of these holes and gaps every day even doing something as simple as ordering fast food or coffee at Starbucks. :-(