Is there a table method that allows you to front load an amount and then decrements as the year prog

Hi,

My client is implementing an HSA plan and for the benefits contribution it is front loaded if you elect a high deductible plan works as follows:

If I am employed at the beginning of the year or hired in the month of January I get 100% of the $500 contribution.

If I am hired in February, I get $458.33 or 91.66%

If I am hired in March, I get $416.66  or 83.32%

If I am hired in April, I get $374.99 or 75%

If I am hired in May, I get $333.32 or 66.64%

If I am hired in June, I get $291.65  or 58.3%

If I am hired in July, I get $249.98 or 50%