Productivity is the careful use of one's resources, including time and money. Most people trade significant amounts of their time for money on a daily basis (e.g., working to earn income), and conversely money can be spent to free one's time (e.g., paying someone else to spend their time on a task).

To make effective time-money tradeoffs, it's important to be able to estimate the value of a marginal hour of one's time.