You can choose to enable auto-renewal when you create a stake. With Auto-renew, you can extend the staking duration and the staking amount for the next period will include previous rewards.
After choosing Auto-renew, you are still allowed to turn off Auto-renew on the staking history section.
If you choose to turn off Auto-renew, you will receive the principal and interest of the first period after the expiration of the term. If you still keep auto-renewing, you agree that the total amount of your principal and interest will be staked for the next period.
This process also applies to subsequent periods.