If your current currency trading broker is in the US, you can check on them to see how much net excess capital they have. The more capital a firm has in excess of the $5 million minimum, the better the protection for your funds.
If you have a non-US fx based broker, check where they are regulated. Europe, Canada, Hong Kong and Australia have strong regulators and capital requirements. If your firm is based in a third world backwater, the regulation may not be particularly strong. You would need to ask why a firm would locate where there is less regulation – is it because they are perhaps less reputable?
To determine the broker’s strength, you should look at the number of employees. If they are a large, strong firm, they will have hundreds of staff who can provide 24 hour support. They should also have tens of thousands of accounts. A firm that has only a handful of staff is unlikely to have a huge capitalization or be able to provide the support you need.
Other factors include the broker’s spreads (the difference between the buy and sell price), and slippage (the difference between the quoted price, and what your order is filled at.
The latter is very important because it is not normally disclosed. In my experience, the worst slippage is when a firm does not actually put your order into the market, but instead trades against you. A firm that does this should be avoided at all costs. It in their interest for you to lose so that they can take your money. I have found that when a position goes my way, it can be impossible to close it out at any price when the fxbrokerage is trading against you.
Find Out More