Pre-pay tithing?

Savannah is such a great wife.  Tonight she wanted to pay our tithing and I said that's great honey.  When she was done, I took the check and looked at it.  It was not the amount of the tithing that we were going to pay, but instead she had written the check for the entire amount of our checking account!  We figured it out and we would have pre-paid tithing for three years!  Can you do that?  Needless to say, we shredded that check and wrote out a new one.