How the loan calculator works
Periodic loan forecast
The forecast uses equal time periods. Nominal annual rates divide by 12, 26 or 52 for monthly, fortnightly or weekly schedules. Effective annual rates convert through compounding. Payment dates label the schedule; the periodic forecast does not charge actual daily interest.
Two repayment systems
Level payments use the annuity formula. Constant principal divides the original financed balance by the term; the interest portion falls as the balance declines. A lower first payment does not necessarily mean a lower total cost.
Fees, insurance and net cash
The amount entered is usable cash. Deducted and financed fees increase financed principal to preserve the usable amount. Upfront fees are separate. Insurance is charged per active period. Compare the same net proceeds, and include residual debt at the selected horizon.
Manual changes and negative amortization
Rate changes and replacement payments are entered manually. Extras apply after the regular payment; recasting changes remaining installments. A payment that does not cover forecast interest can increase debt. The schedule keeps this remaining balance visible.
Budget and actual transactions
The budget uses your chosen reserve, monthly income and expenses. Only available cash above that reserve funds automatic extras; required payments can still produce a deficit. The actual ledger is a separate daily simple-interest model with explicit day-count basis and capitalization. Do not mix the two models when checking a statement.
Checking results
Compare the same date and balance definition with your lender. Rounding, posting dates, allocation, changing rates and contract rules can explain differences. Calculations keep internal precision while displayed money is rounded. For the illustrative $20,000, 12%, 36-month loan without extras, fees or insurance, total scheduled payments are about $23,914.30.
Scope and references
These are educational estimates, not a credit offer or personalized advice. There is no bank connection, automatic market rate, PDF statement OCR or legal APR/CET certification. Reference: Microsoft Excel PMT documentation, linked below. Report reproducible calculation issues through Contact. Last reviewed: 8 November 2026.