Why top up 1k on 2nd day and 3rd $500 out? What's the difference?
Base on my rough understanding:
Assuming last month ur balance is 0,
Then this month the first day is sunday, which I think whatever u transfer will not be in the value date, it will happen on the next day, which is Monday. So, the first day (sunday), compare to the previous month, there is no increment.
Then on day two u add 1k, so this month average is (day one ($ 0) + day two ($ 1k)) / 2 days = $ 500. So ur ADB will be an increment of $ 500 compare to last month. Day 3 if u take out the $ 500, it will be (day one ($ 0) + day two ($ 1k) + day three. ($500) / 3 days = $ 500 (any guru can commend is my understanding correct??

)
For me, my salary is credited on the last day of the month, so on that day, I will transfer out and then transfer $ 500 plus a bit (just in case) on the first day of the month but first few days need to track a bit if they are around weekend or PH.
Now I am thinking of transferring, $ 500 + credit card bill amount, on the first day of the month ( I am using OCBC to pay credit card bills) so that the daily average will be more at the beginning to cover the incremental $ 500 and I pay credit card bills on the 3rd day as I have aligned my all credit card statement date to beginning of the month (DBS / OCBC / UOB). Hope can work, else have to keep tracking.... very troublesome...
So far, I still can get the salary interest, incremental interest and credit card interest.