opensource mortgage modelling tool

opensource mortgage modelling tool

Sep 25, 2026

features:

  • Minimalistic design:

    • virtually no dependencies

    • no need to install anything for local testing / development

  • Super-flexible, yet to get started you only need to provide a handful of figures:

    • House sell price

    • Savings used for down-payment

    • Loan Interest

    • Loan type

  • Supports 3 most popular mortgage types in Netherlands: "Annuity", "Linear" and "Interest-only"

  • Adjustable additional periodic extra repayment schedules, monthly, flexible periodic repayments:

    • you can "program" a monthly additional repayment

    • you can add 3 additional periodic repayments with any periodicity and starting month

  • Adjustable in-place payments (click on any cell in "extra_payment" column in the "Payments schedule"):

    • for already calculated payment schedule you can "change" any payment in-place and schedule will be recalculated from that month onward.

  • Renting, income parameters for assets ROI modelling:

    • takes into account deposit rate, house market growth rate, salary and renting information to calculate monthly total assets state and final "ROI" figures

  • What-if modelling provides uni- and bi-parameter mortgage modelling functionality:

    • to test different loan parameters and to find the most convenient/profitable mortgage configuration

"What-if" modelling:

Allows to model the mortgage as a function of a parameter(s).

  • Any adjustable mortgage parameter can be "probed" on a range of values (e.g. extra monthly repayment).

    • you'll see the parameter variable name when you hover mouse over the input field for it

  • Resulting output parameters of the mortgage then plotted on the graph (e.g. actual mortgage term).

image

Allows bi-parametric modelling.

  • With two parameters being "tested" - target metric drawn on a 3-D surface plot (e.g. Housing assets ROI).

image

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