How to read your result
Total utility is the running sum of satisfaction across everything you've consumed; marginal utility is the extra satisfaction from just the latest unit — while MU is positive, total utility keeps climbing, once MU hits zero you're at the satiation point where total utility peaks, and once MU goes negative, total utility actually falls. Marginal utility usually declines as you consume more of the same good — the law of diminishing marginal utility — which is also one reason demand curves slope downward: each extra unit is worth less, so you'll only pay less for it. When you're choosing between several goods on a fixed budget, watch utility per dollar (MU ÷ price) rather than raw MU: the equimarginal principle says you maximise total satisfaction by spending your next dollar on whichever good gives the highest utility per dollar, continuing until that ratio is equal across everything you buy — MU₁/P₁ = MU₂/P₂ = …, consumer equilibrium. The marginal rate of substitution (MRS = MUX ÷ MUY) is the same idea from a different angle: how much of good Y you'd trade for one more unit of X while keeping total satisfaction unchanged.
Worked example
Six pizza slices with per-unit utility scores of 100, 80, 55, 30, 10, −5.
Total utility running sum: 100, 180, 235, 265, 275, 270. Marginal utility is exactly those per-unit scores — diminishing marginal utility begins at the second slice (MU falls from 100 to 80).
Total utility peaks at 275 on the fifth slice — that's the satiation point (MU ≈ 0 between slices 4 and 5). The sixth slice has negative marginal utility (−5), so total utility falls to 270 — a real cost of over-consuming past the point where extra units stop adding value.
Limitations
Methodology
This calculator computes total utility, marginal utility, and utility per dollar from the scores and prices you enter, and identifies diminishing utility by comparing marginal utility across units. The on-page engine and the Excel workbook formulas are validated against hand-computed cases and an Excel-compatible formula engine on every change. Results reflect your own subjective scores.
- Utility is subjective and ordinal — the scores represent your own ranking, not a physical measurement in real units.
- Cross-good utility comparisons (multi-good module, MRS helper) are only meaningful when all scores use a consistent scale.
- The multi-good allocation follows a greedy equimarginal rule, which is an approximation — it does not account for income effects, substitute goods not listed, or diminishing MU that develops mid-allocation.
- Preferences change with mood, context, time, and habit — a single table is a snapshot, not a model of general behaviour.
- No live consumer data, empirical demand estimates, or professional economic, behavioural, or financial advice.
For the production side of "diminishing" effects, see the diminishing returns calculator — utility is about consumption, returns are about production, and the two are easy to confuse.
Read the guide
There is no dedicated marginal-utility guide yet. The formula section above covers the equimarginal principle and MRS in full.