Mortgage Calculation API

The Mortgage Calculation API performs real-time, data-driven mortgage calculations and Annual Percentage Rate (APR - Jaarlijks KostenPercentage JKP) for the Dutch housing market.

Introduction

The Mortgage Calculation API returns a structured JSON response with a clear mortgage assessment. It is designed for mortgage advisors, banks, and developers who need reliable mortgage calculations, quickly and consistently.

Key features

Key aspects of the Mortgage Calculation API includes:

• Automatic property enrichment: when you provide an address, the API retrieves the WOZ value and energy label. This removes the need to look up the property value manually.

• Nibud 2026 compliant: calculations follow the official Nibud 2026 debt-service-to-income (DSTI) standards.

• Automatic interest rate: if no interest rate is provided, the API fetches the current rate from DNB (De Netherlandsche Bank) automatically.

• Energy label support: providing an energy label applies the official Nibud 2026 extra mortgage amounts and adjust the NHG limit where applicable.

• JKP/APR calculation: calculates the real annual percentage rate, net credit amount, and monthly annuity payment taking into account initial costs.

• Flexible calculation modes:

  • Standard mortgage calculation:

    • With an address: the API uses property data such as the WOZ value.

    • Without an address: the API uses the provided purchase price.

    • Without an address and purchase price: the API performs an income-based calculation and returns the maximum mortgage.

  • Standalone APR (JKP): calculates instantly APR by providing loan amount and nominal interest rate

  • Combined calculation: provide both income and APR parameters to get borrowing capacity and loan credit costs in one call