Does a tax extension give me more time to pay?

No. A tax extension gives you more time to file your return, typically to mid-October, but it does not give you more time to pay. Any tax you owe is still due by the original spring deadline, and interest and a late-payment penalty can accrue on unpaid amounts after that date. To minimize charges, estimate what you owe and pay as much as you can when you file the extension. If you cannot pay in full, look into an IRS payment plan, and consider professional help for large balances.