What the Mortgage Payment Cap and Negative Amortization Calculator is for
Show whether a capped payment covers interest and how the mortgage balance changes over an entered period.
It keeps the property value, balance, cash amounts, rate convention, payment timing, and comparison horizon visible so the result can be checked against an actual quote, statement, budget, or contract.
Calculation structure
Follow the money through time
Each month: ending balance = opening balance + interest at entered rate − capped payment, floored at zero.
Visual explanation
See which inputs change the result
Opening balanceinterest+principalScheduled paymentBalance declines across the entered termEach month: ending balance = opening balance + interest at entered rate − capped payment, floored at zero.
Read the estimate correctly
Use the result with its assumptions
Test whether a 1,000 capped payment covers interest on 300,000 at 6%.
This is a transparent balance path, not a reconstruction of a specific contract. Payment caps, recast triggers, maximum balances, and deferred-interest rules vary.
Quick guide
How to use this calculator
Enter the figures from your mortgage offer, statement, contract, property budget, or scenario.
Keep currencies, rate conventions, periods, and balances consistent; compare multiple plausible scenarios where future rates or costs are uncertain.
Use the component outputs to verify the result and review the calculator-specific boundary before acting.
Calculation method
Calculation method
Each month: ending balance = opening balance + interest at entered rate − capped payment, floored at zero.
Mortgage schedules use stable level-payment arithmetic and advance only the explicitly entered scenario. Results are checked for finite, principal-reducing behavior and round only for display.
Worked example
Practical example
Test whether a 1,000 capped payment covers interest on 300,000 at 6%.
Each month: ending balance = opening balance + interest at entered rate − capped payment, floored at zero.
Supported inputs
Precision and limits
Visible input limits
Amounts are capped at 1e12, rates at 1000% unless a narrower percentage applies, and schedules at 1,200 months unless a frequency comparison explicitly documents more payment periods.
International scope
No currency, country, tax system, mortgage program, lender threshold, insurance rule, market rate, escrow law, or contract term is assumed.
Decision boundary
These are arithmetic scenarios, not offers, approvals, regulated disclosures, forecasts, valuations, legal interpretations, hardship advice, or recommendations.
Calculator-specific assumptions
This is a transparent balance path, not a reconstruction of a specific contract. Payment caps, recast triggers, maximum balances, and deferred-interest rules vary.
