Coin age (Coin age) is a metric reflecting how much cryptocurrency, and for how long, has been held at an address without movement. It is calculated as the product of the number of coins and the time they have been held. For example, if a certain number of coins at an address has not moved for some period, their total "age" accumulates in proportion to both the amount and the duration of holding.

This metric is used in consensus algorithms based on proof of stake (Proof-of-Stake) and its variations. In some systems, the greater the accumulated coin age, the higher the participant's chance of earning the right to create the next block and the reward. After coins are used to confirm a block, their accumulated age is reset and begins to accumulate anew.

The concept of coin age was intended to encourage holders to keep an asset and take part in maintaining the network, as well as to reduce energy costs compared to mining based on computing power. That said, the specific implementation of the mechanic depends on the protocol of each individual cryptocurrency.