About

Why this exists

I built this calculator because I needed it myself. Like many people in the Netherlands, I was trying to decide whether to keep renting or take on a mortgage, and I found that the available tools were either too narrow (US-style spreadsheet calculators ported to .nl with no real understanding of HRA, Box 3, or the Eigenwoningforfait), or too broad (generic "rent vs buy" widgets that ignore tax treatment entirely and just compare rent to mortgage payments). Nothing on the Dutch market combined a realistic mortgage amortisation, the actual annual tax effects of homeownership, and the renter's investment of the down payment in a single, transparent model.

So I wrote one for myself, and then generalised it to two more tax regimes I have connections to (the United States and Italy), both of which have their own rules that off-the-shelf calculators routinely flatten or ignore.

What makes this calculator different

Most rent-vs-buy calculators compare the buyer's home equity against the renter's accumulated rent payments. That ignores the renter's biggest advantage, investing the down payment plus closing costs, and ignores the buyer's actual after-tax cost.

This tool fixes both. Rather than comparing monthly payments, it runs both households forward from the same starting savings and measures their net worth year by year. The full opportunity-cost framing is laid out in the guides and on the methodology page. What makes each country distinct is the tax treatment netted in once a year: the mortgage interest deduction (US), Hypotheekrenteaftrek and the Eigenwoningforfait (NL), the 19% mutuo credit (IT), wealth taxes (Box 3 in the Netherlands, bollo in Italy), and capital-gains tax on the renter's portfolio (US LTCG, Italy's 26% / 12.5% split for equity vs government bonds).

How net worth is defined

For the buyer: home value minus loan balance, plus any portfolio they have accumulated. We do not subtract sale-side transaction costs (agent, notary, transfer tax), which gives an accounting view, not a "if I sold today" liquidation view. For the renter: portfolio value minus the country-specific capital-gains tax that would be owed on liquidation. The two definitions are intentionally asymmetric, to reflect the difference between an illiquid asset and a liquid one.

Inputs and sharing

Every input is encoded in the URL. Copy the share link from any country page to send a complete scenario to a friend, paste it into a doc, or come back to it later. Defaults are filled in for each country so you can land on a page and start exploring without supplying every parameter up front.

Limitations

This is a deterministic model with constant assumed returns and a single appreciation rate. It does not run Monte Carlo over investment outcomes, does not model refinancing or extra principal payments, and treats maintenance and insurance as flat fractions of value. Tax rules are coded as of 2025 and may change. See the Methodology page for the full math, and the Terms for the obligatory disclaimer that this is an educational tool and not financial advice.

Contact

Questions, bug reports, suggestions for additional tax rules to model, or corrections to the math, email financial-instruments@proton.me.