Per scheme, calculate what an investment yields in tax terms: the 40% energy investment allowance, the environmental investment allowance in three categories plus the liquidity benefit of accelerated depreciation, and the small-scale investment allowance with its growth, plateau and phase-out zones — for income tax at your marginal rate or for corporate income tax at the true marginal rate across both brackets.
A 40% allowance sounds like a 40% discount, but it reduces profit — what you actually save is the allowance times the rate that profit would have been taxed at. For a sole trader at 49.5%, a € 20,000 allowance yields € 9,900; for a company it depends where the allowance falls in the brackets. If the allowance crosses the bracket boundary, the effective rate is a blend of both percentages, and the tool computes that blend exactly rather than assuming a single rate.
With the small-scale allowance the surprise lies elsewhere: the benefit is not linear. Up to the first boundary the allowance rises with the investment, then it becomes a fixed amount, and above the second boundary it tapers back to zero. Just past a zone boundary, a larger investment can therefore give a smaller allowance. The tool shows which zone you are in and what that means, and records each outcome with the tool version and the dataset vintage the percentages and boundaries come from.