Lombardkredit vs Box Spread: €100,000 Borrowing Cost Comparison
€100,000 over 12 months. Same borrower, same need, two different financing structures. Here is what each one actually costs in early 2026 — pre-tax, after-tax, and including the parts most comparison tables hide.
The headline numbers
| Item | Lombardkredit (Smartbroker) | Short box spread (ESTX50) |
|---|---|---|
| Posted rate | Euribor + 3.0% ≈ 5.20% | €STR + ≈10bp ≈ 2.10% |
| Gross interest, 12m | €5,200 | €2,100 |
| Tax treatment | Private interest, not deductible | Net loss on the options, offsettable |
| Tax shield (26.375%) | €0 | €554 |
| Net after-tax cost | €5,200 | €1,546 |
| Effective rate | 5.20% | 1.55% |
Rates indicative as of early 2026. Daily numbers on the home-page curve. Smartbroker margin is a representative German broker — Comdirect Wertpapierkredit is similar; DKB and Consorsbank cluster around Euribor + 2–4%.
Where the money actually goes
The headline rate hides four cost layers. Here they are for both:
Lombardkredit
- Interest: €5,200 over 12m at 5.2%.
- Setup fee: typically €0 — most German brokers don't charge for the line itself.
- Hidden cost: nothing — the rate is the rate.
- Tax: nothing offsettable. Private-Schuldzinsenabzug is closed for capital-income use under Abgeltungsteuer.
Short box spread on ESTX50
- Implied carry: €2,100 (the €STR-anchored 12m rate × €100K). A single 500/10000 box only covers about €93K, so you sell two 5,100-wide boxes in one combo order (say 500/5600, quantity 2): about €100,000 in today, €102,000 due at expiry.
- Commissions: ~€8 to open on Eurex (2 contracts × 4 legs at ~€1/contract). Held to expiry, the box settles in cash with no closing trade; allow the same again if your broker charges for settlement. Call it €16.
- Slippage: in our ESTX50 trade data (July–October 2026), small orders filled about 1–2 index points per box below mid, whatever the width. At €10 per point that's €10–€20 per box, so €20–€40 for the two, at most 4 bp on €100K. Split the same loan into fifty 200-wide boxes and you pay it fifty times: €500–€1,000. Close early and you pay it again; details in the risks article.
- Tax: the €2,100 financing cost ends up as a net loss on the options. It is taxed leg by leg: the premiums you receive are income, the settlement at expiry is a loss. The Jahressteuergesetz 2024 removed the ring-fence (including the €20,000 cap), so the net loss offsets dividends, interest, fund income and share gains at 26.375% (about 28% with church tax).
Add it up: box spread total cost ≈ €1,546 (after tax) + ~€16 commissions + ~€30 slippage ≈ €1,592. The friction barely registers: still under a third of the Lombardkredit.
What changes the picture
The €1,546 number assumes you have at least €2,100 in offsetable Kapitalerträge that year. If you don't, the €554 tax shield doesn't materialise immediately — the loss carries forward, and the year-one cost stays €2,100. The Lombardkredit number is unconditional; the box spread number is conditional.
Timing matters too. A 12-month box runs past 31 December: the premiums are taxed in the year you open it, and the loss only arrives in the year it expires. So the €554 saving may come a year later. Plan the cash for it.
What changes the rate itself
The Lombardkredit rate floats with Euribor — when the ECB moves, your bank moves. The box-spread rate floats with €STR — same direction, different transmission. The 3% spread that Smartbroker charges is sticky; €STR-tracked instruments transmit more cleanly.
Concretely: a 100bp ECB cut next year would drop the Lombardkredit roughly 100bp. The box rate would drop similar size, but the gap between them generally widens in falling-rate cycles (term-funding markets price ahead of bank desks).
When the comparison flips
Two scenarios where a Lombardkredit can win:
- Small loan, short tenor. Fill cost and fees are roughly fixed per box, about €15–€30. On €100K for a year that's noise; on a few thousand euros for a few months it can eat the whole rate advantage. Below 3 months, you can't reach a clean Eurex expiry.
- No options account. If you're on a neo-broker and don't want to onboard with IBKR / CapTrader / LYNX, the Lombardkredit is the only line you can actually pull.
Try your own number
Pick a tenor and an amount on the calculator. The numbers above use today's curve; yours will too.
Sources
- § 20 EStG: option premiums (Abs. 1 Nr. 11), Termingeschäfte (Abs. 2 Satz 1 Nr. 3), loss offsetting (Abs. 6)
- Jahressteuergesetz 2024, BGBl. 2024 I Nr. 387, Art. 3 Nr. 7: repeal of § 20 Abs. 6 Sätze 5 and 6 EStG
- BMF-Schreiben of 14 May 2025, Einzelfragen zur Abgeltungsteuer: Rz. 25–35 (options and combination trades), Rz. 118 (loss offsetting)
- § 32d EStG (25% flat tax) and § 4 SolZG (5.5% solidarity surcharge)