How is it not useful?? Isn't the whole point of recommending paying down the higher interest rate loan first is to decrease the amount of interest paid overall?? So how does OP, who is just starting out and learning, know how much they are going to be saving if they don't know how much they would have been paying. I get what you're saying, "duh! it's simple!" but obviously not to OP since they posted the question.

The reason I did the math is to show OP and others who are in similar situations that since they couldn't figure out how much to pay for both, an even split would not be that horrible in the long run. And hopefully save others some time in the future that they can use to be more productive in other ways.

BTW: If OP pays minimum (not sure how long your loan term is, I assumed 10 years) on the lower interest rate and puts the rest of their $1000 towards the higher interest loan the total interest comes to approx $4900. 50/50 split the total interest is 4820.64

The question wasn't to calculate out how much interest would be paid in various options, it was just "how much should go towards each loan", with the reasoning that they are trying to optimize their finances. In that situation the answer is that 100% of available excess funds should go towards the higher interest rate. I don't even have to do the math to know that the most optimal solution is paying the highest interest rate down the fastest.

And speaking of the math:

loan 1 is $21,501 @ 5.16%. Assume 10 years gives monthly payment of $229.74

loan 2 is $20,653 @ 5.9%. Assume 10 years gives monthly payment of $228.25

Option 1 is to split the payment between both, and pay an additional $271.01 on each loan. Last payment is done on payment #47 with an additional $33.39 left over that payment. Total interest paid is $4813.12

Option 2 is to pay loan 2 off fastest. Last payment is done on payment #47 with an additional $162.55 left over that payment. Total interest paid is $4683.45.

An overall difference of about $130.

The exact length of loan, and the exact amount of money saved is somewhat irrelevant though. The main take away is that if you toss everything into a spreadsheet, EVERYTHING will cancel and the only important piece of information is the interest rate. Paying off the highest interest rate as fast as possible is the most optimal solution and will save you the most money. Any other scenario is financially sub-optimal by definition.