At the time of the fiances U.S. Embassy Interview they will be required then to show the sponsors financial affidavit of support together with all supporting documents. Your have to count yourself as 1 and count your alien fiancee as 1 which gives you 2.
But if the sponsor has dependents then they must also be counted and if the alien fiancee has children coming under the K2 visa then they also have to be counted.
If it is just the sponsor and the beneficiary you need $16,020. to show at the interview but after your fiancee is married to you it changes to $20,025. unless you live in Hawaii or Alaska or if you are in the U.S. Armed forces? you may go to uscis.gov and research I-864P