Penalties & Interest
The IRS and state punishes those who file and pay their taxes after the due date by enforcing the tax penalty and interest. There are many tax penalties including the failure-to-file and failure-to-pay penalty.
The penalty for failure-to-file a tax return by April 15th (or the extended due date) is 5% of your tax liability for each month, for a maximum of 25%. The failure-to-pay your taxes by April 15th (an extension to file does not grant an extension to pay) is 0.5% of your tax liability for a maximum of 25%. However, if you have reached the maximum penalty amount of 25% for failure-to-file, you will not incur an additional 25% failure-to-pay penalty. Instead, your maximum penalty for both will be 25% of your tax liability.
Even though you cannot afford paying your taxes, you should still consider filing your tax return because the failure-to-file penalty is significantly greater than the failure-to-pay penalty. Also, an installment agreement will reduce any future failure-to-pay penalty from 0.5% to 0.25% of your tax liability.