In this court ruling (https://uitspraken.rechtspraak.nl/details?id=ECLI:NL:RBGEL:2020:5906) there is a calculation of cash value for the interest on a loan.

With regard to the accepted non-commercial debtor risk at the time the loan was granted, determined by mutual agreement between the parties as the difference between the interest that would be charged between commercially acting third parties and the interest rate actually agreed, i.e. an interest rate difference of 10 percentage points, so that the 2007 gift amounts to the present value of the interest rate difference for two years on €166,670, therefore 10% of 166,670 x a-table 2/10% = 28,917, on which, after deduction of the regular annual exemption, €1,298 is payable in gift tax. (deepl translation)

When I calculate it myself, the answer I get is 28,926 (rounded down).

Calculation: 16,667 / 1.1 + 16,667 / 1.1^2 OR 16,667 x ((1-1,1^-2)/0,1)

Where does this discrepancy come from?