Spousal maintenance is awarded in Missouri in some cases. There is no formula for the calculation however, and the award of maintenance is determined on a case by case basis. A rule of thumb is that the marriage must be lengthy (10 years or so — but this is not a legal requirement), and there is a large difference in income between the parties. Spousal maintenance is based on need and ability to pay, and is not used as a punishment for misconduct during the marriage. The duration of the maintenance may be limited or unlimited, depending on the circumstances.