Calculators

Mortgage calculator

Available on each region detail page. Computes:

• Monthly payment using standard amortization formula
• Total paid over the loan term
• Total interest paid

Default values are prefilled from the region’s data (flat price, current mortgage rate). If a scenario is active, values are prefilled from the scenario instead.

Formula

P = principal * (r * (1+r)^n) / ((1+r)^n - 1)

Where r = monthly rate, n = number of months.

Savings calculator

Also on each region detail page. Computes years to save the full flat price by investing monthly savings at a given return rate.

Uses the future value of annuity formula:

n = ln(1 + target * r / pmt) / ln(1 + r)

Where r = monthly rate, pmt = monthly savings amount.

HTMX integration

Both calculators use hx-post to submit the form and replace the result div with an HTML fragment returned by the server. No JavaScript framework needed.