Paysaurius Open Decision Engine

Calculator

The Mortgage Decision Engine

You have extra cash and a mortgage. Enter your numbers once and compare prepaying, recasting, refinancing, and investing — ranked by projected net worth, with the trade-offs spelled out.

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

    How to use the Decision Engine

    1. Enter your current mortgage — balance, rate, and years remaining.
    2. Add your extra cash — a lump sum, a monthly amount, or both.
    3. Open the advanced sections to add a refinance offer or investing assumptions.
    4. Read the four cards — the highlighted one saves the most interest. Then weigh the caveats.

    How it works

    Each strategy is computed with a standard fixed-rate amortization model. Prepaying applies your cash to principal and keeps your payment level; recasting re-amortizes the lower balance over the same term; refinancing builds a new loan and finds the closing-cost breakeven; investing projects an after-tax future value to compare against the guaranteed savings of prepaying. Full formulas are on our methodology page.

    Learn more

    Frequently asked questions

    What does the Decision Engine compare?

    It compares four uses of extra cash on your mortgage — making an extra principal payment, recasting, refinancing, and investing the money instead — plus your current 'do nothing' baseline, all on the same screen.

    How is the recommendation chosen?

    Strategies are ranked by projected net worth at a common horizon (the baseline payoff date), giving each path the same lump sum and the same monthly budget so the comparison is fair. We always surface non-financial factors too — liquidity, emergency funds, and risk — because the math alone shouldn't make the decision.

    Is my data sent anywhere?

    No. Every calculation runs in your browser with JavaScript. There is no backend, no database, and no analytics that tracks your inputs. Your numbers never leave your device.

    Are the results financial advice?

    No. They're educational estimates based on the figures you enter and simplifying assumptions (fixed rate, level payments, no PMI or escrow). Verify with your lender and a licensed professional.