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 offsetable Kapitalerträge to absorb the Termingeschäft loss.
- 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 carry of a short box spread is a Termingeschäft loss under §20 EStG. Post-JStG-2024 it offsets fully against other Kapitalerträge (dividends, realised stock gains, interest) at the Abgeltungsteuer rate of 26.375%.
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.
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.