Total utility is maximum when marginal utility is zero.

Basic idea

In consumer theory, total utility (TU) is the overall satisfaction obtained from consuming a given quantity of a good or service, while marginal utility (MU) is the extra satisfaction gained from consuming one more unit.

As you consume more units, marginal utility usually declines (law of diminishing marginal utility), so:

  • When MU > 0, each new unit still adds to total utility → TU is increasing.
  • When MU = 0 , the last extra unit adds nothing → TU has reached its peak.
  • When MU < 0, extra units even reduce overall satisfaction → TU starts falling.

Simple numerical illustration

Here is a stylized mini‑table:

Units consumed| Total utility (TU)| Marginal utility (MU)
---|---|---
1| 10| 10
2| 18| 8
3| 24| 6
4| 28| 4
5| 30| 2
6| 30| 0
7| 29| –1

TU reaches its highest value (30) at unit 6 , precisely where MU falls to zero ; beyond that TU falls as MU becomes negative.

So the precise statement is:

Total utility is maximum when marginal utility is zero.

Information gathered from public forums or data available on the internet and portrayed here.