Paysaurius Open Decision Engine

Free · private · no sign-up, ever

You've got cash and a mortgage. What's the smart move?

Pay it down, recast, refinance, or invest the money instead — four very different answers, and most calculators only show you one. Punch in your real numbers and see all four ranked side by side. It runs entirely in your browser; nothing you type ever leaves your device.

Run my numbers ↓ Or start with a guide

Built by Marcus Hale after one very long weekend with a spreadsheet. The math is tested to the cent.

The Decision Engine — go ahead, try it

Four moves, one screen, your numbers

Type in your mortgage and your spare cash below. It ranks the options by the net worth you'd actually end up with, and tells you plainly what each one costs you in flexibility. No email wall, no waiting.

Your current mortgage
$
%
yr

We convert this to months automatically.

Your extra cash
$

Cash you could apply now (used for prepay, recast & investing).

$
Refinance offer (optional)
%
yr
$
Investing assumptions (optional)
%
%

Used to estimate after-tax investment return.

$

Extra Principal

—

projected net worth

Monthly payment
—
Total interest
—
Interest saved
—
Payoff
—
Fees
—

Recast

—

projected net worth

Monthly payment
—
Total interest
—
Interest saved
—
Payoff
—
Fees
—

Refinance

—

projected net worth

Monthly payment
—
Total interest
—
Interest saved
—
Payoff
—
Fees
—

Invest Instead

—

projected net worth

Monthly payment
—
Total interest
—
Interest saved
—
Payoff
—
Fees
—

Projected net worth by strategy

Higher net worth at the horizon is better

Before you decide

    Prefer a single-purpose tool? Open the full Decision Engine page, or browse all six calculators.

    The four moves

    One pile of cash, four honest paths

    There's no universally "best" one — each solves a different problem. The trick is knowing which problem is yours.

    1. 01

      Pay down the principal

      Throw the cash at the balance, keep paying the same amount, and watch years fall off the loan.

      Extra payment calculator →
    2. 02

      Recast it

      Same rate, same finish line, smaller monthly bill. The quiet option most people have never heard of.

      Recast calculator →
    3. 03

      Refinance

      Trade your loan for a new rate and term — worth it only if you clear the closing-cost breakeven.

      Refinance calculator →
    4. 04

      Skip the mortgage, invest instead

      A guaranteed return from prepaying versus a probably-bigger one from the market. We show you the line where they cross.

      Read the breakdown →

    Why I built it this way

    Nothing leaves your browser

    There's no server collecting your balance and income, because there's no server at all. The whole thing is a static page that does math on your device.

    All four on one screen

    Most sites hand you a single calculator and a "talk to a lender" button. You can't decide between options you can't see together — so here they're together.

    Honest about the unknown

    Prepaying is a sure thing; the market isn't. I keep those two clearly apart and never pass off a forecast as a promise. See the methodology.