Calculation rules

Interest will be calculated by applying to the amount of the undue deduction the late payment interest rate in force in each of the fiscal years between the due date of the declaration period for the fiscal year in which the undue deduction was made (or, where applicable, from the day following the date on which the refund was obtained) and the date on which the declaration corresponding to fiscal year 2023 is submitted.

The sum of the late payment interest corresponding to each of these years will determine the total amount of late payment interest corresponding to the undue deduction.

For these purposes, three periods can be distinguished when determining late payment interest:

• Initial period

It will include the number of days elapsed from the day after the end of the declaration period corresponding to the year in which the deduction that is now being restored was made (or, where applicable, from the day after the date on which the refund was obtained) and December 31 of said year.

The determination of the amount of late payment interest for this period can be carried out using the following calculation formula:

Interest on initial period delay = Deduction amount x (interest rate ÷ 100) x (period (number of days) ÷ 365 or 366)

The interest rate, expressed as a percentage of 100, will be the late payment interest rate in force in the fiscal year to which the initial period corresponds.

• Intermediate period

It will cover each of the complete years following the initial period, until December 31, 2023.

The determination of late payment interest corresponding to each of the calendar years included in this period can be carried out using the following formula:

Interest on arrears for each year = Deduction amount x (interest rate ÷ 100)

The interest rate, expressed as a percentage of 100, will be the late payment interest rate in effect in each of the years comprising this period.

However, since the same late payment interest rate (11%) was in force in 1994, 1995 and 1996, the interest corresponding to those years that form part of the interim period may be determined globally by multiplying the aforementioned late payment interest rate by the number of said years that make up the aforementioned period. This same rule may be applied in the years 1999 and 2000 for which the same rate of late payment interest was in force (5.5 percent); for the years 2002 and 2003 in which the same rate of late payment interest was in force (5.5 percent); for the years 2005 and 2006, in which the same late payment interest rate was in force (5%) and for the years 2008 and 2009 (until 31 March 2009), in which the late payment interest rate was 7%. From April 1, 2009 to December 31, 2014, the late payment interest rate is 5%. The late payment interest established for the year 2015 was 4.375 percent; for 2016, 2017, 2018, 2019, 2020, 2021 and 2022, 3.75 percent, and for the years 2023 and 2024, 4.0625 percent. 

• Final period

It is the period between January 1, 2024 and the date of filing the declaration for the 2023 fiscal year (July 1, 2024).

The determination of the interest corresponding to this period can be carried out using the following formula:

Late payment interest final period = Deduction amount x (4.0625 ÷100) x (T24 ÷ 366)

T24 represents the number of days of the delay period included in the year 2024, that is, those elapsed between January 1 and the date of filing the declaration for the 2023 fiscal year.

Note: For 2024, the late payment interest rate of 4.0625 percent applies until the General State Budget Law for 2024 is approved and comes into force, which may establish a new interest rate.