Portfolio Loan Calculator Germany: After-Tax Effective Rates
A portfolio loan calculator that shows the German after-tax effective rate, not just the gross. The home-page calculator is free, no signup, and updates every trading day.
What the calculator shows
Three numbers, every time:
- Implied gross rate for your tenor — interpolated from today's box-spread curve on SPX (USD) or ESTX50 (EUR).
- After-tax effective rate — the gross rate × (1 − 0.26375) on the assumption that you have capital income to absorb the loss on the options.
- Money cost in your currency — the absolute carrying cost over your tenor on your principal.
Inputs
- Currency — EUR (ESTX50, Eurex) or USD (SPX, CBOE). The rate, the contracts, and the tax treatment all flow from this.
- Amount — what you want to borrow. €25K minimum is sensible; commissions and slippage matter less above that.
- Tenor — how long you want the financing. The calculator clamps to 1–36 months and snaps to the nearest tradable Eurex/CBOE expiry when generating the leg structure.
What "after-tax effective rate" really means
In Germany, the financing cost of a short box spread ends up as a net loss on the options. It is taxed leg by leg: the premiums 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 fully against other capital income (dividends, interest, fund income, gains from selling shares) at the Abgeltungsteuer rate of 26.375%, or about 28% with church tax.
The shield only materialises in years where you have offsetable Kapitalerträge. The calculator displays the full-shield case; if your situation is different, mentally floor the after-tax rate at the gross rate.
Timing matters too. If the box runs past 31 December, the premiums are taxed in the year you open it and the loss arrives in the year it expires. The saving may come a year later, so plan the cash for it.
Outputs
Beyond the headline rate and money cost, the calculator generates:
- The four-leg structure — exact strikes, expiry, contract count, and limit price for the closest tradable box.
- Copy-to-clipboard text for paste into IBKR Trader Workstation notes or your trading log.
- Target vs. actual — if the closest tradable box doesn't exactly match your input amount, the calculator shows the gap (typically under 5%).
What the calculator doesn't do
- It does not place trades. It computes; you execute. Read-only by design.
- It does not factor in commissions or slippage. Add ~€100–500 per €100K position depending on size and tenor.
- It does not check your specific tax position. The 26.375% shield assumes offsetable Kapitalerträge are available.
- It does not check your broker's margin requirements. Portfolio Margin or Eurex SPAN is required for the rate to be economically meaningful.
How to read the result
If the after-tax rate is materially below your bank's Lombardkredit (5%+ in early 2026), the gap is the savings — minus your execution friction. On €100K over 12m, the typical headline gap is €1,500–€3,000 of cost, well above the €100–€500 friction. The calculator's job is to show you the headline gap; the friction estimate is on you.
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)