This calculator applies the monthly rate to completed calendar months and the daily rate to remaining days under Article 51 of Law No. 6183. You can use dates or enter whole months manually.
What is the late payment surcharge (gecikme zammı)?
The late payment surcharge is a monthly surcharge rate applied under Law No. 6183 on the Collection Procedure of Public Receivables (various public receivables other than tax, administrative fines, etc.) when they are not paid on time. The rate is set periodically by the Ministry of Treasury and Finance and can change.
Date-mode formula: Principal × (Monthly Rate / 100) × (Whole Months + Remaining Days / 30). Article 51 requires partial months to be calculated by day.
Where do I find the current rate?
The monthly rate is 3.7% from 13 November 2025 under Presidential Decision No. 10556. Date mode automatically selects the rate from the supported GİB period table; manual mode uses the rate you enter. A date range spanning an official-rate change is refused and must be calculated in separate segments.
What is the difference between gecikme zammı and gecikme faizi?
Gecikme zammı and gecikme faizi (late payment interest) are two distinct mechanisms in Turkish public receivables law; gecikme faizi is generally a separate mechanism specific to tax assessments. This tool calculates only gecikme zammı; a separate tool is needed for tax-specific gecikme faizi calculations.
What does this tool not calculate?
- It does not automatically split a period across multiple official rates; calculate those segments separately.
- It does not calculate tax-specific late payment interest (gecikme faizi) or rules specific to other types of public receivables.
Frequently Asked Questions
How is the late payment surcharge calculated?
Completed months use the monthly rate; remaining days use the daily rate obtained by dividing the monthly rate by 30.
Does this tool know the current surcharge rate?
In date mode, the tool automatically selects the monthly rate from its supported GİB period table beginning 1 January 1990. Periods before 1990 are not supported, because the official table sets them as tiered schedules rather than a single monthly rate. Manual mode uses the rate you enter; verify the applicable rate with GİB before official use.
How are partial months counted?
Partial months are not rounded up. After completed months, remaining days use the daily rate equal to the monthly rate divided by 30.
Are gecikme zammı and gecikme faizi the same thing?
No, they are distinct mechanisms in Turkish public receivables law. This tool calculates only gecikme zammı.