Step 1
At the end of every day, IB will obtain the following balances in each currency:
 Ending Settled Cash balance in the securities account segment
 Ending Settled Cash balance in the commodities account segment
 Collateral balance for settled short stock positions
 Ending Settled Cash balance in the IBUKL segment
 Commodity risk margin requirement
The cash balances are reported on the Daily Statement under Ending Settled Cash. The commodity risk margin requirement is the Maintenance Margin Requirement as reported on the daily Margin Report minus the total commodity option value.
The collateral balance per short stock is calculated by multiplying the prior day's closing price by an adjustment factor based on the currency, rounding this value up, then multiplying by the number of shares.
For example, the collateral balance on a USDdenominated security would be:
Collateral Balance = (stock A prior day closing price x 102%, rounded up to the nearest 1.00) x (number of shares stock A) + (stock B prior day closing price x 102%, rounded up) x (number of shares stock B)
The adjustments utilized by IB are as follows:
USDdenominated stock – multiply by 102%, round up to nearest 1.00 
CADdenominated stock – multiply by 102%, round up to nearest 0.50 
EURdenominated stock – multiply by 105%, round up to nearest 0.01 
CHFdenominated stock – multiply by 105%, round up to nearest 0.01 
GBPdenominated stock – multiply by 105%, round up to nearest 0.01 
SEKdenominated stock – multiply by 105%, round up to nearest 0.01 
AUDdenominated stock – multiply by 105%, round up to nearest 0.01 
HKDdenominated stock – multiply by 105%, round up to nearest 0.01 

Step 2
IB collects the overnight reference interest rate that will serve as the benchmark (BM) on which subsequent calculations are made. More information about these benchmarks is available here.
Step 3
IB calculates an Adjusted Cash Balance for the universal account by combining the Ending Settled Cash balances for the securities, commodities and IBUKL segments and subtracting the commodity risk margin requirement as well the short stock collateral value. The commodity risk margin requirement is removed from interest considerations as this represents margin which may be put up at the exchange rather than being considered free funds.
AdjustedCash = EndingSettledCash_Securities + EndingSettledCash_Commodities + EndingSettledCash_IBUKL – ShortStockCollateralValue  CommodityRiskMargin
Step 4
IB will then determine how much of the AdjustedCash balance should be applied to each rate tier (see tier tables). Finally, we calculate the interest using the applicable rates (also from the tier tables):^{ 3}
The numberOfDaysInYear are based on industry standards for money market activity.
 365: AUD, CAD, CNH/CNY, GBP, HKD, KRW, ILS, INR, NZD, RUB, SGD
 360: USD, EUR, CHF, CZK, JPY, SEK, NOK, DKK, HUF, MXN
( Balance _{tier1} * Rate _{tier1} / numberOfDaysInYear ) 

( Balance _{tier2} * Rate _{tier2} / numberOfDaysInYear ) 

( Balance _{tier3} * Rate _{tier3} / numberOfDaysInYear ) 

etc 
