How can I get an extension on paying my federal taxes?

There are no extensions to pay.  If you can pay it off in less than 3 months, just be late.  The IRS will bill you for interest and late fees.  If you will be more than 3 months late, you can apply for a payment plan on the IRS web site.  This reduces the penalty somewhat, but there is a non-refundable processing fee for the payment plan, so if you can pay in less than 3 months, the penalty is probably less than the application fee.  Don't apply for a payment plan in turbotax, the fees are higher.  Make sure you file on time.  The penalty for late filing is 10x higher than the penalty for late paying.