How to calculate as precise as possible the amount you receive in a spot order api

I'm using the binance API from Python to place spot orders, I've noticed a difference between how much I expect to receive and how much I receive.

For example I want to trade 1000 ADA with the pair ADA/BTC with a value of 0.000016. I've got a standard account without BNB fee discount, so the fee should be 0.10%

New_btc_amount = (1000 * 0.000016) * 0.999

Otherwise if I want to trade 0.01 BTC in the same pair I do:

New_ada_amount = (0.01 / 0.000016) * 0.999

Am I missing something? Is there a round problem? How can i calculate this with more precise results?