Short Answer:

If you miss both the tax filing and payment deadlines, the IRS will charge both late-filing and late-payment penalties along with interest on unpaid taxes. The late-filing penalty is typically 5% per month of unpaid taxes, while the late-payment penalty is 0.5% per month, both capped at 25%.

Interest accrues daily on unpaid balances from the original due date. The longer you delay filing and payment, the higher the total cost, and repeated failures can trigger IRS audits or collection actions such as liens or wage garnishments.

Detailed Explanation:

Consequences of missing filing and payment deadlines

1. Late-filing penalties

The IRS imposes a late-filing penalty when a tax return is not submitted by the due date, including extensions if one was not filed. This penalty is calculated as 5% of unpaid taxes per month or partial month, up to a maximum of 25%. It applies even if some taxes are paid, and it accumulates monthly until the return is filed.

Late filing is considered more serious than late payment because it affects IRS recordkeeping and prevents the accurate calculation of taxes, deductions, and credits. Failing to file increases the likelihood of audits or substitute returns prepared by the IRS.

2. Late-payment penalties

If taxes owed are not paid by the original deadline, the IRS charges a late-payment penalty of 0.5% per month on the unpaid balance. This penalty also accrues monthly and can reach up to 25% of the total unpaid tax.

Even if the return is filed late, any unpaid tax continues to accrue late-payment penalties until fully paid. The combination of late-filing and late-payment penalties can significantly increase your financial liability.

3. Interest on unpaid taxes

Interest is charged daily on any unpaid taxes from the original due date, typically April 15. Interest accrues regardless of filing status or extensions and compounds over time.

• Interest continues until the full tax is paid
• Partial payments reduce principal, which can lower interest accrual
• Combined with penalties, interest can quickly increase the total amount owed

4. Collection actions

If taxes remain unpaid for an extended period, the IRS may initiate collection actions to recover the debt. Possible actions include:

• Bank levies to seize funds directly from your account
• Wage garnishments to take a portion of your paycheck
• Tax liens on property to secure unpaid taxes

These actions can have long-term financial consequences and affect credit and personal finances.

5. Refund delays

Failure to file on time can also delay refunds, even if you overpaid taxes. If both filing and payment are late, the IRS may take longer to process returns, calculate interest, and issue any refund.

6. Mitigating the impact

To reduce penalties and interest:

• File your return as soon as possible, even if late
• Pay taxes owed immediately or set up an installment plan with the IRS
• Keep accurate records of payments and submissions
• Request penalty abatement if reasonable cause exists for delays

Even after missing deadlines, taking prompt action reduces total financial exposure.

7. Special considerations

Certain circumstances may provide relief from penalties:

• Reasonable cause, such as illness, natural disasters, or unavoidable events
• First-time penalty abatement for taxpayers with a clean record
• IRS relief announcements in extraordinary situations

However, interest on unpaid taxes usually continues regardless of relief.

8. Planning to avoid missed deadlines

To prevent missing both filing and payment deadlines:

• Prepare returns early and gather all documents in advance
• Use estimated tax payments if self-employed or with multiple income sources
• File for an extension if necessary and pay estimated taxes to reduce penalties
• Track deadlines carefully using calendars or tax software

Proper planning avoids penalties, interest, and potential IRS enforcement.

Conclusion:

Missing both tax filing and payment deadlines results in late-filing and late-payment penalties along with interest on unpaid taxes. Delays increase financial liability and can trigger IRS collection actions or audits. Filing and paying as soon as possible, even after missing deadlines, reduces additional charges and ensures compliance with IRS rules.