How to write off the Down Payment in rental income?

Hi, i have a question regarding rental income properties: if i put let say 20% down to buy a rental property how can i write off this amount from the end of year balance? let say income 1000/month, and expenses(mortgage, repair, etc) 800/month what happens to the down payment? it is an expense afterall to... show more Hi,
i have a question regarding rental income properties:

if i put let say 20% down to buy a rental property how can i write off this amount from the end of year balance?

let say income 1000/month, and expenses(mortgage, repair, etc) 800/month

what happens to the down payment? it is an expense afterall to run the rental income business? no?

if i cant write off the amount, then what if i take only 10% down, it brings up the mortage and of course i will pay less taxes at the end.

i am missing the logic.

thanks
henri
Update: thanks for all the answers, very helpfull
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