Most online calculators simulate a single mortgage.
Cascade is a browser-based simulator for comparing repayment strategies across two mortgages.
It models how:
- Applying overpayments using the avalanche method (highest interest first)
- (Optional) Redirecting scheduled payments and/or overpayments once one of the mortgages is paid off
And shows how this impacts:
- 🕒 Time to become mortgage-free
- 💰 Total interest paid
Cascade compares three scenarios:
- While both loans are active, any overpayments target the higher-interest mortgage
- After one loan is paid off: scheduled payments and/or overpayments can be redirected to the remaining loan
Each mortgage keeps its own overpayments. No redirectign money from one mortgage to another at any point.
Standard amortisation with no voluntary extra payments, and mortgages run separately.
- Mortgage-free date
- Total interest paid
- Months saved
- Interest saved vs separate
- Balance-over-time chart
- Year-by-year payment flow
The app is split into clear layers:
engine.js— Pure financial logic (no DOM manipulation)chart.js— Chart rendering (Chart.js wrapper)app.js— UI controller (reads inputs, renders results)
(The UI calls one function in engine.js to run all calculations)
calculateCascade(
m1,
m2,
extra1,
extra2,
redirectScheduled,
redirectExtra,
"avalanche"
)- Monthly compounding
- Standard amortisation formula
- 2 decimal rounding
- No fees, penalties, tax modelling, or lender rules are incorporated
This is a modelling tool — not financial advice.
Most mortgage calculators handle one loan.
Cascade is useful for:
- Two people combining finances
- Investment property strategies (e.g. someone who owns two properties)
- Overpayment allocation decisions
- Redirect mechanics after payoff
Clone the repository and open index.html in your browser.
No build step required.
Built as a side project.
Results are estimates, not guarantees.
Always confirm important financial decisions with a qualified adviser.