How it works
The calculator starts with your home value and the maximum LTV allowed for your cash‑out program. Many conventional cash‑out refis cap the new loan at around 80% of the home’s value. Max loan allowed = Home value × Max LTV %. This is the largest new loan amount your lender is likely to permit, subject to underwriting.
From that maximum loan, we subtract your current mortgage balance and the closing costs you plan to finance to estimate the cash you can take out. Cash‑out available ≈ Max loan allowed − Current balance − Closing costs. If this value is negative, we floor it at zero to reflect that no usable cash is available under those assumptions.
The new loan amount is modeled as the sum of your current balance, closing costs, and any cash you receive, but never exceeding the maximum allowed by LTV. New loan amount = min(Max loan allowed, Current balance + Closing costs + Cash‑out). In practice, this ensures the cash‑out plus closing costs fits within the LTV limit.
To compute the new payment, the calculator uses a standard fixed‑rate amortization formula. Based on your selected new interest rate (APR) and new term in years, it converts the annual rate to a monthly rate and multiplies the years by 12 to find the term in months. It then calculates the monthly principal‑and‑interest payment that fully amortizes the new loan over that term.
Next, the calculator estimates your current payment path. Using your current interest rate, original term, and current balance, it approximates your current monthly P&I payment and multiplies it by the months remaining (original term months minus months already elapsed) to estimate how much you would pay if you stayed on your existing loan.
From those remaining payments, it backs into the remaining interest on your current path by subtracting your current balance from the total remaining payments: Current interest remaining ≈ (Current payment × Months remaining) − Current balance. This represents the interest you still owe if you do not refinance.
For the new loan, it computes total paid as New payment × New term months and subtracts the new loan amount to find total interest over the new term: New interest over term ≈ (New payment × New term months) − New loan amount.
Finally, the calculator reports the difference between your new monthly payment and your current payment, along with both interest figures. This lets you see whether the cash‑out refi will increase or decrease your payment and how the lifetime interest on the new loan compares to the remaining interest on your current mortgage.