Box Spread Instead of a Mortgage? What It Can and Can't Do
A box spread is a way to borrow. Can it replace a mortgage? Mostly no. But it can do some of the jobs around buying a home, often cheaper than the alternatives.
How does it work?
Options are financial instruments you can buy or sell on the open market. With the right combination of four of them you get a synthetic loan: cash in your account today, and a fixed amount to pay back on a set date. The rate is set by the market, close to what large institutions pay to borrow.
There are plenty of resources online, and we have an in-depth, step-by-step guide if you want the mechanics. You can see today's rates on our daily curve.
What it can do
- Fund the down payment without selling. If your savings are invested, selling them for the down payment can trigger tax and takes you out of the market. Borrowing against the portfolio instead keeps it invested, and you pay the box back later from income, a bonus or a planned sale.
- Bridge a purchase. Buying the new place before the old one is sold? A box can cover the gap for a few months, and you repay it when the sale closes. Our bridge calculator compares it with a bank bridge loan and with selling investments.
- Lower the mortgage you need. A larger down payment can mean a smaller mortgage, or a better rate on it.
What it can't do
- It isn't secured by the house. Your portfolio is the collateral, not the property. If markets fall hard, your broker can ask for more margin or sell positions, even while the house is fine.
- It doesn't last 25 years. A box runs for months or a few years. To borrow longer you roll it into a new one at whatever rate the market offers then. That behaves more like a variable rate than a long fixed-rate mortgage.
- Your lender will want to know. Banks ask where the down payment comes from, and money borrowed against your portfolio can count as debt when they check what you can afford. Tell them up front.
How much to borrow
Keep the loan a modest share of your portfolio. Our calculators use 25–30% of the portfolio as the ceiling, so that a crash like early 2020, when markets fell by about a third, doesn't force a sale at the bottom. Less is safer.
The box itself doesn't move with the market, but the portfolio holding it up does. That is the real risk of this approach.
Taxes: every country is different
The cost of a box shows up as an investment loss, not as mortgage interest, and each country treats that differently. In some it reduces tax on your other investment income; where mortgage interest is deductible, a mortgage can still come out ahead after tax. Our country guides explain how it works in Germany, Spain, France and the US.
Try the numbers
Our property calculator compares three ways to fund a purchase: borrowing with a box, selling investments, or paying cash. It is built around German purchase costs, so adjust the assumptions to your country.
This is general information, not financial or tax advice. Check your own situation with your bank and a tax adviser before you commit to a home purchase.