NAF Interest Calculator
Calculate legal interest for overdue taxes and social security!
NAF interest calculator
Estimate legal interest on overdue public liabilities
Principal, due date and payment date
Informational label only; formula unchanged in MVP.
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What does the NAF interest calculator calculate?
The NAF interest calculator is an online tool that calculates legal interest for overdue taxes and social security contributions to the National Revenue Agency (NAF), based on the reference interest rates of the Bulgarian National Bank (BNB). The calculator shows the total amount you owe to NAF, including the principal, overdue interest, and total amount to pay. The calculator is useful for legal entities and individuals who have overdue obligations to NAF and want to understand the exact amount to pay, for accountants calculating obligations for clients, and for everyone planning to settle debts to NAF. It helps you plan your financial future and make informed decisions about settling obligations.
How to use the interest calculator?
The interest calculator helps you calculate legal interest for overdue taxes and social security to NAF, based on current reference interest rates.
- Enter principal: Enter the amount of overdue tax or social security contribution in BGN.
- Select obligation type: Specify whether it's tax or social security (different types have different interest rates).
- Enter dates: Enter the due date and the actual payment date (or today's date).
- Calculate: Click "Calculate" and the calculator will show results.
- Review results: View overdue interest and total amount to pay.
Example with specific numbers
Example: Overdue VAT - 5,000 BGN, 60 days overdue
- Principal: 5,000 BGN
- Obligation type: VAT (tax)
- Due date: January 15
- Payment date: March 16 (60 days overdue)
- Interest rate (BNB reference): ~3.5% per year
- Overdue interest: 5,000 × (3.5% / 365) × 60 = ~28.77 BGN
- Total amount to pay: 5,000 + 28.77 = 5,028.77 BGN
For overdue VAT of 5,000 BGN with 60 days overdue, the overdue interest is approximately 28.77 BGN (at BNB reference interest rate ~3.5% per year). Total amount to pay is 5,028.77 BGN. Interest rate varies according to current BNB reference interest rates and obligation type.
Sources and notes
The calculator uses current reference interest rates of the Bulgarian National Bank (BNB) for calculating overdue interest. Interest rate is calculated as daily interest (annual rate / 365 days) multiplied by the number of overdue days. Interest rates vary according to obligation type (taxes, social security) and current BNB rates. It's important to note that specific interest rates may change according to legislation and BNB policy. For accurate calculations and current interest rates, always consult with NAF or an accountant. The calculator provides an estimated assessment and does not replace official calculation by NAF.
Last updated: April 3, 2026
Data is up to date according to NRA and NOI (Bulgarian tax and social security). For official information see the sources below. Last update: 3 April 2026.
Sources:
- NRA – National Revenue Agency
- NOI – National Social Security Institute
- VAT Act – Bulgarian VAT law
- Local taxes act – Local taxes and fees
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Frequently Asked Questions
What is legal interest?
Legal interest is interest charged on overdue tax and social security obligations to NAF, calculated based on BNB reference interest rates.
How is interest calculated?
Interest is calculated as daily interest (annual rate / 365 days) multiplied by the number of overdue days from the due date to the payment date.
What are the current interest rates?
Interest rates are based on BNB reference rates and vary by obligation type. Rates may change, so always check with NAF or an accountant for current rates.
Do I need to pay interest if I'm late?
Yes, if you pay taxes or social security after the due date, you must pay legal interest on the overdue amount for each day of delay.
How accurate is the calculator?
The calculator provides an estimate based on current BNB rates. For official calculations, always consult with NAF or an accountant, as rates and regulations may change.