Interest uses the opening balance
Each period’s interest is calculated before principal reduction, so earlier extra principal normally prevents more future interest than the same amount paid later.
Dated amortization, rate-reset, and prepayment strategy
See how every payment changes principal, interest, and the payoff date
Build a dated monthly schedule with two rate resets, automatic recasting or a retained payment, recurring, annual, and one-time extra principal, origination-cost APR, a constant-rate baseline, and explicit maturity balance.
Plan with context
An amortization schedule is a contract timeline, not merely a repeating formula.
Each payment responds to the opening balance, current rate, contract method, calendar position, and any extra principal. Modeling those events exposes payment shock, interest savings, negative amortization, and maturity risk.
Rate resets need contract mechanics
Adjustable loans can change with an index and margin subject to caps, floors, lookbacks, and rounding. Entered resets are scenarios, not forecasts.
Recasting and retaining differ
Recasting recalculates payment over the remaining term after a rate change. Keeping the original payment can accelerate payoff or fail to cover new interest.
Extra principal has several patterns
Recurring additions, annual lump sums, and one-time payments affect different months and should match cash that is realistically available.
Negative amortization increases debt
When a retained scheduled payment is below accrued interest, the unpaid amount increases principal unless contract rules require another treatment.
A maturity balance stays visible
If the strategy does not reach zero by the contractual end, the remaining balance is shown instead of being silently extended beyond maturity.
Included
Dated monthly schedule, years and months, initial rate, two entered rate changes, recast or retained payment, monthly extra with start month, annual and one-time extra principal, original fixed-rate baseline, payoff dates, interest and time savings, origination-cost cash-flow APR, payment-change table, Chart.js balances and cumulative interest, and full ledger.
Not included
Live rate indexes, rate and payment caps, floors, lookback dates, daily accrual, escrow, late fees, payment holidays, lender-approved recast fees, modification, bankruptcy, partial-payment suspense, tax effects, or an official payoff quote.
Use it well
Copy the rate-change and payment rules from the note, reconcile the opening balance and next due date to a statement, confirm how extra funds are applied, and request a formal payoff amount before settlement.