I filed my Form 1120-S by March 15 but haven't paid taxes. What's the penalty and interest?

If you filed Form 1120-S by the March 17 deadline but have not paid the taxes due, the IRS will charge a penalty of 0.5% per month (or part of a month) on the unpaid tax amount. This penalty can accumulate until it reaches a maximum of 25% of the unpaid balance. However, the penalty may be waived if you can show reasonable cause for not paying on time.