Greetings. I am not (yet) a T-Mobile customer. I have a question about purchasing a new phone from T-Mobile.

In the first attachment, I show that T-Mobile is offering a $1,000 promotion for my trade-in - the Samsung Galaxy S23 Ultra 5G in good condition - if I purchase a new Samsung Galaxy S25 Ultra on an EIP.

In the second attachment, I show that the full retail price of the S25 Ultra with 256GB of storage $1,299.99. Thus, if I apply my $1,000 promotion, I should pay $299.99 for this phone after all is said and done.

The second attachment also shows that my monthly payment for the 24-month EIP will be $20.83. But $20.83 x 24 months = $499.92, not $299.99!

It's a little misleading, however, because T-Mobile actually doesn't apply the $1,000 promotion evenly over the 24 months of the EIP. According to T-Mobile's website, I'll get a one-time bill credit of $320, and the $680 balance of the promotion with be divided evenly among the 24 months of the EIP. Let's see the arithmetic in that case:

$1,299.99 - 320.00 = $979.99 - 680 = $299.99 / 24 months = $12.50 per month. This is less than the $20.83 per month that T-Mobile advertises!

So my question is: How does T-Mobile calculate a monthly payment of $20.83??

This question has stumped three different T-Mobile customer service reps, but then I shouldn't expect them to know anything about the calculation of monthly costs, since their purpose is to sell and that is how they are trained.

Can anyone explain how the $20.83 per month is calculated?