Tax Penalty

Full explanation

The IRS imposes several types of penalties: Failure to file (5% of unpaid tax per month, up to 25%), Failure to pay (0.5% of unpaid tax per month, up to 25%), Underpayment of estimated tax (variable rate, currently ~8%), Accuracy-related (20% of underpayment for negligence or substantial understatement), and Fraud (75% of underpayment). Penalties are in addition to interest, which accrues daily on unpaid tax. You can request penalty abatement for reasonable cause (first-time penalty abatement is commonly granted). File even if you can't pay — the filing penalty is 10x the payment penalty.

Source: IRS Topic 653 — Penalties