re: I'm struggling to figure out if refinancing makes sense for my situation.

Check out that calculator I linked. It can give you all the numbers you want to know. I was in your situation earlier in the summer. 7 years into a 3.625% mortgage and I didn't really want to mess with a refinance, but I could just never make the numbers favor not refinancing.

Without knowing the original principal and if you've always paid $400 extra, I had to kind of guess. So I'm assuming your original loan was around $225k and you've paid $400 extra since inception. This gives a current balance of around $207k. Here's what the remainder of that mortgage looks like if you continue paying $400 extra.

Payoff in 16 years
The remaining balance is $207,134.42. By paying extra $400.00 per month, the loan will be paid off in 16 years. It is 10 years earlier. This results in savings of $47,053.81 in interest.

If Pay Extra $400.00 per month
Monthly Pay $1,426.12
Total Payments $322,347.75
Total Interest $97,347.75
Remaining Payments $273,094.21
Remaining Interest $65,959.79

The Original Payoff Schedule
Monthly Pay $1,026.12
Total Payments $369,401.55
Total Interest $144,401.55
Remaining Payments $320,148.01
Remaining Interest $113,013.59


Here is $207k on a 15 with $5k in closing costs rolled in (so financing $212k) at 2.25%.


Normal loan repayment without extra payments:
Monthly Pay $1,388.78
Total Payments $249,980.35
Total Interest $37,980.35


If you pay the extra $37/month on the 15 year to make the payments match, you shave 5 more months and about $1000 in interest off.


Payoff in 14 years and 7 months
The remaining balance is $212,000.00. By paying extra $37.00 per month, the loan will be paid off in 14 years and 7 months. It is 5 months earlier. This results in savings of $1,219.16 in interest.

If Pay Extra $37.00 per month
Monthly Pay $1,425.78
Total Payments $248,761.19
Total Interest $36,761.19