Marginal Utility is found by taking the difference between successive Total Utility figures.

MU: $14,\ 26-14=12,\ 36-26=10,\ 44-36=8,\ 48-44=4,\ 48-48=0,\ 44-48=-4$. MU falls at every step (14,12,10,8,4,0,-4), so the Law of Diminishing Marginal Utility holds throughout.

Marginal Utility of the $n$-th unit is the addition made to Total Utility by consuming that unit: $MU_n = TU_n - TU_{n-1}$ (taking $TU_0 = 0$).

The MU column falls continuously — 14, 12, 10, 8, 4, 0, −4 — with no reversal at any step, so the Law of Diminishing Marginal Utility is fully confirmed by this schedule. Notice also the TU–MU link: TU keeps rising exactly as long as MU stays positive, TU is at its MAXIMUM (48) precisely at the 6th cup where MU first becomes zero, and TU actually FALLS at the 7th cup because MU has turned negative there — the consumer is now so full that an additional cup of tea makes him feel worse off, not better.

A frequent error is computing Marginal Utility as Average Utility (TU divided by the number of units) instead of the DIFFERENCE between successive TU values — the two give very different numbers and only the difference is the correct definition of MU. Another common slip is stopping the schedule at the point TU is maximum and failing to notice that MU can legitimately go negative beyond that point.