Dividends are calculated off of the average daily balance in the account. If the account exceeds $14,999.99(Rewards) or $19,999.99(RewardsPlus) then you will see a "Split Rate", this may make the rate appear lower than what the you are actually getting.
RewardsPlus checking
((19,999.99 x 0.0198) ÷ 365) x days in month
+
((Balance over 19.999.99 x 0.0005) ÷ 365) x days in month
Rewards checking
((14,999.99 x 0.0149) ÷ 365) x days in month
+
((Balance over 14.999.99 x 0.0005) ÷ 365) x days in month