Finnish tax card includes so called basic taxation percentage. That will be used in taxation till the cumulative salary during the validity period reach the limit. When cumulative salary exceeds the limit, the extension percent will be used for taxation.
Limit: 47000 €
Salary: 5000
Basic percentage: 25
Extension percentage 49
As long as the cumulative salary stays under 47000, the tax will be 5000 * 25 % = 1250. If the cumulative salary exceeds 47000 then the tax will be 5000 * 49 % = 2450.
If limit is exceeded but only partially, the salary will be taxed by basic percentage till the limit, and the part exceeding the limit will be taxed per extension percentage.
If cumulative salary during the validity period before the payment is 46000, then 1000 of the salary will be taxed per 25 % and remaining 4000 per 49 % equaling to (1000 * 25 %) + (4000 * 49 %) = 2210.

The IF-sentence is here for copy paste:
=IF(D8-D3 >=D4;D4*D7;IF(AND(D8-D3>0;(D8-D3<D4));(D8-D3)*D7+(D4-(D8-D3))*D9;IF(D8<=D3;D4*D9)))
You might find some other IF-sentence for the same purpose. This is just my example.






