Interest follows balance
Interest is calculated from the outstanding principal and periodic rate. Early principal reductions avoid interest over more future periods than equally sized late reductions.
Mortgage ledger and payoff engineering
Audit every principal dollar, rate change, recast and extra-payment milestone.
Build the baseline amortization, add recurring and one-time principal, model a future rate reset and optional recast, then solve for the monthly extra needed to hit a target payoff date.
Decision guide
How to read an amortization schedule
Amortization is the month-by-month allocation of each payment between interest and principal. Small timing changes can alter both the payoff date and lifetime cost.
Recast is not refinance
A recast re-amortizes the remaining balance at the existing rate and remaining term. Refinancing replaces the loan and can change rate, term and closing costs.
Rate resets change the path
When the rate changes, the required payment may be recalculated to retire the remaining balance on schedule. Stress-test that payment before the reset arrives.
Direct extras to principal
Confirm how the servicer applies additional funds and whether the next due date advances. Keep statements showing each curtailment.
Protect liquidity
Mortgage prepayment is difficult to reverse. Compare guaranteed interest savings with emergency reserves, other debt and investment alternatives.
Escrow is separate
Taxes, insurance and HOA costs do not reduce the loan balance. They are included only for the ownership-budget projection and may rise independently.
Simple by design
Three steps to a clearer number.
Enter your details
Use realistic values in each field. You can change them anytime.
Calculate instantly
The formula runs locally, so there is no account or waiting time.
Use the result
Treat the answer as a practical estimate for your next decision.