When is consumer in equilibrium and maximizing total utility?

A consumer is in equilibrium and maximizing total utility when they allocate their budget in such a way that the marginal utility per dollar spent on each good is equal across all goods consumed. This condition is known as the equi-marginal principle, where the last unit of currency spent on each good provides the same additional satisfaction. At this point, the consumer has no incentive to reallocate their spending, as any change would lead to a decrease in total utility.