About
About Paysaurius
A small, opinionated tool for one of the most common money questions there is: I've got some extra cash and a mortgage — now what?
The short version
A few years ago I had a little money saved up and a 30-year mortgage, and I couldn't get a straight answer about what to do with it. Pay the loan down? Recast it? Refinance? Just dump it in an index fund? Every calculator I found answered a quarter of the question and then tried to sell me a refinance. So I did what any reasonable person with too many spreadsheets would do, and built the thing myself. That thing turned into the Decision Engine.
What I'm trying to get right
Three things, mostly. The math has to be correct — not "close enough," but right to the cent, which is why every formula on this site is covered by automated tests. Your numbers have to stay yours, so nothing you type ever leaves your browser; there's no server collecting it because there's no server at all. And the trade-offs have to be honest: prepaying earns a guaranteed return, investing might earn more but might not, and I'll never dress up a forecast as a promise.
What you won't find here: lead-capture forms, "get matched with a lender" buttons, or your email being quietly sold to a broker. I find that stuff exhausting too.
Who writes this
I started Paysaurius after burning a long weekend on spreadsheets, trying to decide whether to throw a bonus at our mortgage or invest it. The advice online was either a sales pitch or a single-purpose calculator that answered half the question. So I built the tool I wished I'd had. I'm not a licensed advisor — I'm a stubborn person who likes getting the math exactly right and showing my work.
To be clear about what I'm not: I'm not a licensed financial advisor, mortgage broker, or accountant, and nothing here is personal advice. Think of Paysaurius as the spreadsheet you'd build for yourself if you had the time — a starting point for a conversation with your lender and, if your situation is complicated, a professional who knows it. The methodology page shows every formula and assumption, because a money tool should show its work.
How this stays free
Hosting a static site costs me almost nothing, so for now Paysaurius is simply free. Down the line I may add a few clearly-labeled ads to cover the bills — but never lead-gen forms, and never selling your data. If that ever changes, it'll be said plainly here and in the privacy policy first.
Found a mistake?
Please tell me. If a number looks off, send me the inputs you used and what you expected on the contact page — getting the math right matters more to me than being right, and corrections genuinely make my week.
Paysaurius provides educational estimates only and is not a lender, broker, or financial advisor. See the full disclaimer.