If you want to get extra fancy you can also try to calculate the opportunity cost difference between the payments and refinance cost (if applicable).

I'll look up how to get extra fancy. In the meantime, here's what I got:

I'm using the basic loan calculator from Excel. It isn't exact, but it's close (I'm saying this because it says I should owe $88000, and I owe $88,300 right now).

On our most recent payment, we paid $657 principle ($490 of which is the extra payment we make, so $167) and $343 interest. It moves a couple dollars a month toward principle. Assuming we sell the house in June and that June is the last house payment we make, if we

1. change nothing, we'll pay $6050 in principle, $2956 in interest

(Payment: $1000 June balance: 82.3k)

2. stop paying extra, keep our loan, we'll pay $1640 in principle, $2956 in interest

(Payment: $511 June balance: 86.7k)

3. refi for exactly $1100 to 3.25% with a balance of 88.3k, and roll it into the loan for a total of 89.4k and don't pay extra on the principle: $1333 in principle, $2160 in interest

(Payment: $389 June balance: 88,063)

4. refi for $1100 to 3.25% with a balance of 88.3k, pay $1100 upfront, $1320 principle, $2138 interest

(Payment: $384 June balance: 87k)

Soooo. . . by going from 2 to 3, we lower our monthly payment by $122, which we are able to save 10/1 to 6/1, for a total of $1,098. We'll have a loan balance that is $1363 higher than we would have if we had just switched to plan 2 (we're currently doing 1). So it'd end up being $165 more expensive to refi than to do plan 2, not accounting for what that $122 could do for us in VTSAX over those 9 months, which I do not know how to figure.

By going from 2 to 4, we free up ~$1150 in payments, but we have to pay $1100 upfront. This one doesn't seem to be desirable to us at all based on my math.

All that said, is there a compelling reason to stop doing plan 1 and do something else?