Box Spread Financing in Spain, Explained Simply
Box spread financing means borrowing. Not from your bank, but from the options market, against the portfolio you already hold.
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.
There are plenty of resources online, and we have an in-depth, step-by-step guide if you want the mechanics.
Why the rate is low
You are funding yourself at very low rates because of how these instruments are priced. The market sets the price, close to what large institutions pay to borrow, without a bank's lending margin on top. You can see today's rates on our daily curve.
No market risk, if done correctly
If done correctly, a box spread is immune to market movements. Whatever the index does, you know in advance how much you will pay back at expiry.
Done correctly means European-style, cash-settled index options such as the S&P 500 (SPX) or the Euro Stoxx 50, all four legs placed as one order, and enough margin headroom. The box itself doesn't move with the market, but your other positions can still trigger a margin call.
Taxes: every country is different
Each country treats this differently. In Spain it works like this:
- The cost is a capital loss. What you pay for the loan shows up as a loss on the options, a pérdida patrimonial in the savings income base (base del ahorro). It counts in the year the box closes or expires.
- It offsets your gains first. The loss offsets gains from selling shares or funds without limit. Whatever is left offsets up to 25% of your dividends and interest, and the rest carries forward for 4 years.
- The saving is your savings-income rate. That is 19% up to €6,000, 21% up to €50,000, 23% up to €200,000, 27% up to €300,000 and 30% above.
- A foreign broker won't do it for you. Interactive Brokers doesn't withhold Spanish tax, so you declare the result in your Renta. If your foreign accounts and securities add up to more than €50,000, check your modelo 720 obligation.
There is no ruling from the tax authority specific to box spreads; the general treatment of options applies. This is how the law reads today, not tax advice. Check your own situation with a tax adviser. Our Spanish tax page has a calculator.
Sources
- Ley 35/2006 del IRPF: art. 37.1.m (options results are capital gains and losses), art. 49 (offsetting and 4-year carryforward), arts. 66 and 76 (savings-income rates)
- Dirección General de Tributos, binding rulings V0512-19 and V0503-21: options results belong to the savings income base
- AEAT, Manual práctico de Renta 2025: futures and options
- AEAT, Manual práctico de Renta 2025: offsetting in the savings income base
- AEAT, modelo 720 FAQ