Tax Extension Penalty Calculator
Calculate penalties and interest for IRS tax extension underpayment.
Extension Details
Penalty Analysis
Estimated Tax
$$15000.00
Payment Made
$$0.00
Underpayment
$$15000.00
Penalty + Interest
$$1050.00
Underpayment Penalty
Payment below safe harbor minimum of $$13500.00. Penalties: $$450.00 + interest $$600.00. Pay at least 90% of estimated tax by Apr 15.
Safe Harbor Rules
90% Safe Harbor
$$13500.00
Pay 90% of current year tax
100% Safe Harbor
$$15000.00
Pay 100% of previous year (110% for AGI over $150K)
Extension Deadlines
Personal (Form 4868)
Original: April 15. Extension: Oct 15 (6 months)
Business (Form 7004)
Original: March 15. Extension: Sept 15 (6 months)
Penalty Rates
Failure-to-pay penalty: 0.5% per month (max 25%). Interest: 4% annually (variable rate). Penalties accrue from original deadline even with extension. File extension to avoid failure-to-file penalty (5%/month, max 25%).
Key Points
Extension extends filing deadline, NOT payment deadline. Must estimate and pay tax by original deadline. Separate state extension may be required. File extension even if can't pay - avoids larger filing penalty. Penalty abatement possible for reasonable cause.