Most banks will charge you for doing that. Mine charges $35 if I don't have enough money. Better just let the sale go through.

The ACH won't go through and the order will be cancelled with Coinbase. They may flag your account too and make it harder to buy in the future. Please rate them and your experience here too: http://bitcoinx.io/exchanges/coinbase

You get the fine from Chase for an over-draw on your account because of insufficient funds when Chase pays the ACH. What is that $25.00 now? It was afterall an authorized ACH.

I bought some BTC on coinbase.com less than 24h ago. I was not aware you cannot cancel a purchase even though it has not gone trough and the money is still in my bank account.

I bank at chase, if I take the money out of the account now, what will happen when Coinbase tries to take the money by ACH? Will the transaction simply be declined for insufficient funds?

I mean I can't see how it would go through. For example, if I have 19.90 in my account and try to take out 20.00 it won't even let me overdraft the account so why would it in this case?

Thanks