How it works
Spread is calculated as half the difference between the bid and offer prices for the contract traded. The percentage rebate is calculated from the tier applicable to each month's trading, based on the notional USD volume traded that month.
For example, in January you open and close a transaction for 10 contracts of USD/JPY ($1 million notional) which has a pip value of JPY 10,000. Your total volume in the month was $330m so you are in the tier 2. The rebate paid for this individual transaction is therefore:
JPY 10,000(pip value) x 1.2(spread) x 10%(rebate) = JPY 1,200 (converted to $11.21 at an exchange rate of 107 JPY per USD)