Just a note - Canada and USA are very different wrt morthgages - in Canada, you take out, say, a “25 year morthgage with a 5 year term” when the term is up, you refinance at current market rates. Rising interest is starting to bite homeowners here as the new rates become applicable upon mortgage renewal.
In the USA, you take out a mortgage for the life of the mortgage, with a fixed rate for that life. Interest is allegely deductible (not in Canada).
Canadian mortgages typically limit pay-down to 10% of original principal, and ability to double up payments. I assume your US mirtgage has no such limits.
Another important point to consider. What’s your marginal tax rate (i.e. on each extra dollar you earn)?
If you invest and make 5%, but pay (let’s say) 25% of those earnings in taxes, you only made 3.75% take-home. For $25K, 5%=>$1250, 25% tax=>$412.
If you pay down your mortgage, $25K is roughly 1/5 of $120K. So, you are paying $5604 or so in interest over a year. Subtract $25K from that debt, and you are paying $4,436 a year. (of course, this changes as you pay things down, and because of monthly calculation, yada yada) So, $1168 less of interest to deduct. If it can be deducted at marginal tax rate, $1168x1/4=$292. (Assuming you can deduct)
About $300 vs. $400, the break even is close over a year. Just with one, you don’t owe on the house much sooner. With the other, you may have a huge amount of resultant investment. “Rule of 70” says roughly(!) within 70/(interest rate) years, your money should double. 70/5=14. In 14 years you’d have $50K instead. Asuming (!!!) you can get a consistent 5% from the markets. They go up, they go down.
Another consideration, what investment? If you keep some cash around for a rainy day but invest, how easy is it to get the money out on short notice. Can you handle needing a new furnace, or air conditioner, or replacing the roof shingles? (Things we’ve done in the last 10 years on a relatively new house) My wife’s uncle was managing her grandmother’s money, and when she died there were some bonds that did not mature for a year, holding up the estate distribution. Usually the better and less risky investments hav lock-in provisions.
if it were me, I’d put $15K on the house and hold $10K in reserve. If you are confident your parents can cover or loan any emergency funds, then put down the whole amount. Myself, I prefer not being in debt so paying off the house is a priority.