Quick guide
How to use this calculator
- Enter amounts from the same property scenario and use consistent periods and units.
- Use visitor-entered rates and allowances from your own documents rather than assuming a local rule.
- Review the component results and the calculator-specific decision boundary before acting.
Calculation method
Calculation method
Period interest = (opening debt + draw timing share × draws − repayment timing share × repayments) × periodic rate.
Entered fixed decimals remain exact through rational arithmetic. Planar distance outputs that require square roots use bounded numerical evaluation. Values round only for display, and unsupported or undefined states return an explicit message.
Worked example
Worked example
A 1% monthly rate on 1,000,000 opening debt with 200,000 mid-period draws uses an average balance of 1,100,000 before repayments.
Period interest = (opening debt + draw timing share × draws − repayment timing share × repayments) × periodic rate.
Supported inputs
Precision and limits
International scope
No currency, market price, interest rate, tax, tenancy rule, planning code, lender policy, or measurement definition is supplied automatically.
Scenario, not a decision
Results are arithmetic scenarios from visitor-entered values—not an appraisal, loan approval, legal interpretation, planning determination, forecast, or professional recommendation.
Precision and privacy
Inputs accept bounded plain decimals and remain in this browser. The engine prevents invalid denominators and misleading non-finite results.
Calculator-specific boundary
The entered timing convention is a scenario, not a lender method; compounding, fees, day-count and eligible draw rules may differ.
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