President Trump’s recent suggestion for a 50-year mortgage fueled a storm of opinions online. Some think it’s a wild idea, but let’s see what the numbers say before rushing to judgment.

The biggest allure of the 50-year mortgage is the lower monthly payment. For the average U.S. home price of $415,200 (with a 10% down payment and 6.17% interest rate), your monthly payment on a 30-year loan would be about $2,288, while a 50-year mortgage drops that to $2,022. That makes it easier for first-timers and stretched households to enter the market.

However, that upfront relief comes at a hefty long-term cost. Over the loan’s life, someone choosing a 50-year mortgage would pay close to $389,000 more in interest than they would on a standard 30-year mortgage. That’s nearly the price of a whole other house in many places.

Building home equity also slows dramatically with an ultra-long loan. On a 30-year mortgage, it takes around 12-13 years to gain $100k in equity (excluding down payment and home appreciation). For a 50-year mortgage, it’s more like 30 years before you hit the same milestone.

Supporters claim the 50-year loan could help more people qualify for a mortgage, perhaps even spurring more housing construction. Critics warn it could create a new generation of permanent borrowers, locked into lifetimes of payments with painfully slow wealth accumulation. Affordability won’t improve just by stretching out the loan term—it’ll take wage gains and stabilizing home prices.

So, is a 50-year mortgage nuts? It depends on what matters to you: lower payments now, or paying off your house (and actually owning it) before retirement. Before signing up, run your own numbers with a mortgage calculator and weigh the true cost to your financial future.