Let’s start by talking about borrowing money from the bank. You went to a local bank A and borrow $ 100 in your country currency as say its United State Dollars. This bank A charge you 5% interest yearly. Your friend goes to another bank B and borrows $ 100 United State Dollar at 2% interest yearly. So if you want to borrow another $ 100 and your friend lend it to you at 5% interest (he took loan $ 100 from another bank). By simple calculation, your friend is effectively earning 3% interest. (5%-2%=3%). If you hold on to this for 1 year, you are carrying over your trades over a year and yield you 3% interest rate on the principle amount.
Sound similar to carry trade?
Imagine your friend is the broker. You put money into your trading account instead of borrowing from banks, your broker account will reflect $ 100 (assume the earlier example, you put in $ 100.) and this is in United State Dollars. Since you are holding currency in your trading account, it is incurring interest from the government that issue that currency. Eg United state is giving 2% interest. On the other hand Japan Yen is giving 0.5% interest. So if you borrow Japan Yen to buy equivalent United State Dollar, you will gain 1.5% interest yield every year. (Or use United State Dollar to Sell Japan Yen.)
So total how much you will earn?
Assume you use $ 100,000 and use it on the carry trade between United State Dollar and Japan Yen, giving you 1.5% yearly, which work out to be $ 1,500. If your trading account is using 100:1 leverage, you are effectively using your original $ 100,000 to buy and hold $ 10 million, which give you $ 150k a year. This work out to be 150% Return On Investment.
Can this work in real life?
Of course there are few factors to consider before your 150% Return On Investment can be realized. Avoid margin call, the currency fluctuation and the exchange rate between United State Dollar and Japan Yen. Let’s start by taking the positive direction, the exchange rate is rising for (assuming you get 5% more Japan Yen if you sell), the currency fluctuation is at minimum of near 0% drawdown and no margin call. You can earn $ 150k + $ 500k = $ 650k about 650% Return On Investment.
But this is always not the case
The currency rate went down (assuming you get 1% less Japan Yen if you sell). The currency fluctuated 1% drawdown. You earn $ 150k - $ 100k = $ 50k. but before you can realized your profit of 50K, you are hit will margin call of 1% ($ 100k) and your trade are call out within a week, which leaves you almost zero. And I mean zero dollars. Now you see the risk of forex trading using leverage. Of course I simplified a lot of the calculation and conversion. But it is enough to make you understand the basic of carry trade and interest rate.
Always take charge by calculating money management into every trade you execute. Keep it to 10% of your capital. For the earlier example, you should only use $ 20K to buy $ 1 million forex currency which potentially could yield profit of $ 65k or loss $ 35k (assume drop of 5% with 1.5% interest difference on the carry trade).
Which currency then?
There no recommended currencies to buy, but you have to look out for currency with the highest interest rate, currency with the lowest interest rate and a trending up exchange rate when you sell back. (buy low, sell high). Always remember to use money management calculation (assume 10% of your capital with 100:1 leverage)