# Investeer.ing

> Investeer.ing is a Dutch company game. Visitors read five sourced historical facts, choose whether they would have bought at the start of 2026, then reveal the company and its historical share price outcome through 4 September 2026. Returns use split-adjusted closes in the listing currency, excluding dividends, costs, taxes and FX. A rising price rewards buying; a falling price rewards passing, compared with cash at 0%. A fixed collection of 100 companies is sampled randomly on each visit or refresh, preferring unfinished companies. After each answer, visitors can continue immediately. Choices stay on the device. This is an educational game, not a stock recommendation.

The existing Rendement-rekenmachine remains available at /rendement.

Canonical website: https://www.investeer.ing/
Language: Dutch for the Netherlands (`nl-NL`)
Calculation year: 2026
Last reviewed: 2026-08-17

## Use the calculator

- [Interactive calculator](https://www.investeer.ing/rendement): Human-facing calculator with shareable query parameters.
- [JSON calculator API](https://www.investeer.ing/api/rendement?amount=10000&grossRate=7&costRate=0.35&inflationRate=2&kind=beleggen&partner=false): Stateless machine-readable result.
- [OpenAPI specification](https://www.investeer.ing/openapi.json): Parameters and response contract for agents and applications.
- [Full method and boundaries](https://www.investeer.ing/llms-full.txt): Formula, official inputs and interpretation guidance.

## Important boundaries

- Results are educational one-year indications, not personal financial or tax advice.
- The entered amount is treated as the complete Box 3 asset base, without debt or special exemptions.
- The tool uses the 2026 provisional Box 3 percentages published by the Dutch Tax Administration. The savings and debt percentages become final in early 2027.
- Investment returns are user assumptions and are never forecasts, promises or recommendations.