All addresses that contain at least one Algo, which is the current Minimum Earning Unit (MEU), are eligible to receive rewards. The rate of participatory rewards in the Algorand protocol is changing frequently, so it is difficult to derive an exact and enduring formula for reward calculations.
Generally, an account earns tokens every block, but the rewards are only credited and are not claimed until an event like a transaction impacts that account. For example, if Alice sends Algos to Craig’s existing account, that transaction will have a fromReward field that claims the Algos that have been credited to Alice’s account since their last event, and a toReward field, that does the same for Craig.
In the unlikely event that you miss rewards, we cover lost rewards with our 100% reward guarantee.