How do I know what the APR is for my on-chain Slate staking rewards?

The Swipe Slate on-chain staking rewards are calculated in real-time based on the protocol distribution of the daily SXP reward rate. This is dynamic and subject to change due to the protocol being external on the blockchain and in real-time, but the Swipe Wallet will have an estimate APR displayed in the Swipe SXP Wallet asset screen.