IB interest calculation?

getting a little confused with the calculation.

lets pretend John day trades and has $200K cash in his IB account.

at a 4.25% benchmark rate(1/3/08).

to me it looks like John accrues per day:

Tier Balance
<10,000 interest = 0.00
10K-100K interest = 9.375 [90K x (4.25%-0.5%)/360]
>100K interest = 11.11 [100K x (4.25%-0.25%)/360

thus $20.485/day

http://individuals.interactivebroke...nterestMethods.php?ib_entity=llc#calculations
http://individuals.interactivebrokers.com/en/accounts/fees/interest.php?ib_entity=llc

can someone confirm on how this is calculated?
 
I tried your calculation using my last statement. Using the prior day's settled cash and your calculation, I was a bit off. I did it again using 365 days (instead of 360) and got within 1 cent.
 
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