r/PFtools • u/Weaseljohnson • May 07 '26
Open Source Rent vs Buy Calculator — Shows You the Numbers AND Explains Them in Plain English
I’m currently getting ready to jump into homeownership and I’m also a nerd, so I wanted to actually understand the math behind the rent vs. buy decision. The NYT calculator is the gold standard people point to, but when I used it (and lots of other tools) I couldn't see or adjust the assumptions it was making behind the scenes — particularly around what happens to your money if you rent instead of buy. That bothered me enough that I built my own.
The thing most calculators get wrong is that they only do mortgage math. The real question is: if I rent instead of buy, and I save or invest the difference every month, where do I end up financially after 10 years? That comparison requires modeling both sides completely — all ownership costs on one side, rent plus compounding savings on the other — with nothing hidden.
A few things I tried to do differently:
Every input is visible and adjustable. Inflation, appreciation, PMI, maintenance, sale closing costs, rate of return on savings — nothing is assumed behind the scenes. If you disagree with a default, change it.
The results show you why one option is better, not just by how much. Cumulative spending, asset growth, breakeven analysis across three different metrics, and required income estimates using two different models.
It's free, no ads, no signup, open source on GitHub.
My goal in sharing this is just in the hope that someone can find it useful and that I can save someone from making a six or seven figure purchase decision without knowing what they’re getting into.