Calculate refinancing of fixed Danish mortgages with and without "instalments"/afdrag.

Use on desktop, there's a lot of tables and numbers. https://mathiastj.github.io/mortgage-refinancer/

To see an example of converting up from 1% to 4% interest check: https://mathiastj.github.io/mortgage-refinancer/?example=1

To see an example of converting down from 4% to 2% interest check: https://mathiastj.github.io/mortgage-refinancer/?example=2

I wanted to calculate the breakeven point of refinancing my mortgage. The Totalkredit app has a calculator, but it doesn't take into account the extra 8% tax deduction of interest payments up to 50k/100k. The loan offers sent from my bank did not take this into account either.

I started out with an Excel sheet, but figured this would be a fun little project, and I also think it gives a better overview.

I wanted to try out React Hooks and Tailwind CSS with a Next.js setup.

• Correctly use the 8% extra tax deduction on interest and "bidrag" payments. Takes into account whether the mortgage is financed by a single person or a couple.
• To correctly calculate the 8% extra tax deduction it's possible for the user to enter their other interest payments per year.
• Choose municipality for correct municipality and church tax.
• Shows breakeven point in years of when the principal of the new loan exceeds that of the old.
• Shows breakeven point of when monthly payments after taxes in total for the new loan have exceeded that of the old.
• Shows breakeven point of when monthly payments after taxes for the new loan have exceeded that of the old for a year.
• Automatically calculates "bidragssats" (extra charges) for the new loan, based on estimated price of the house and the new loan amount.
• Show the price with or without "kundekroner", a discount on the "bidragssats" (extra charges).
• Easily compare old and new loan in two tables next to each other.
• Switch from an instalment free loan to one with instalments, or the other way around.
• Select mortgage institute from the 4 large Danish providers for the new loan. Makes it easy to compare the "bidragssats" (extra charges) between the institutes.

Here's a screenshot from desktop: