How does this affect your forex trading account?

If you are long the currency bearing the higher interest rate then you should earn interest, automatically credited to your trading account. Conversely, if you are short the currency bearing the higher interest rate then you should experience a small debit to your account.

Be aware that most forex brokers require a 2% margin set for your account in order to receive interest. If not, you will have to pay for the rollover, it doesn't matter whether you are long or short the currency bearing the higher interest rate

Day Traders

For day traders, who almost never hold any overnight positions, the rollover is not applicable because there are no positions to roll, and therefore no interest is earned or paid.

Swing Traders

If you are a swing, position or long term trader, the rollover will affect your account since you'll earn or pay interest on a daily basis. Therefore, it is recommend to set your account at 2% margin and only try to long the currency bearing the higher interest rate.

A strategy for the longer term trader is the carry trade, which relies on a big interest rate differential between the two traded currencies.
For example the NZD/JPY currency cross pair.

Currently, traders earn a $13 daily rollover interest, credited to their accounts at 5PM EST while holding a long position in this pair for each standard lot(1 standard lot equals 100,000 units) traded; BUT, if you are short NDZ/JPY, your account will be debited $14/day for each standard lot traded! Interesting fact to know, isn't it?

Rollover example

If you are long 300,000 EUR/USD at rollover (5PM est) and EUR/USD at rollover is trading at 1.3200, the EUR short-term interest rate is 3.50% and the USD short-term interest rate is 5.25%

Forex Market Daily Interest Rollover

In the spot fx market, trades settle in two business days and open trading positions held at time of rollover are automatically rolled over by the forex broker to the next settlement date, the open trade position is swapped for a new position expiring the following settlement date at 5pm EST rollover. This is also known as "tomorrow, next day" or simply "tom next."

For example, if you buy 200,000 Euros on Monday, you must deliver 200,000 Euros on Wednesday. On Wednesdays, the amount added or subtracted to an account as a result of rolling over a position tends to be around three times the usual amount. This "3-Day" rollover accounts for settlement of trades through the weekend period.