The goal of Big Paydays is to give WHEAT stakers the incentive to stake for longer periods!
The Big Paydays bonus gives an extra 1.5% of the staked amount for each complete 30-day period staked! You have to complete 30 days to get each 1.5% bonus, and it is claimable when the stake's entire staking period is complete.
You get this in addition to the regular bonus tokens from Staking!
Here are the Big Payday Bonus and total bonus WHEAT amounts you receive from various staking periods: