There is one unpleasant fact for you to take into consideration about the margin call Forex. You might not even receive the margin call before your positions are liquidated. If the money in your account falls under the margin requirements, your broker will close some or all positions, as we have specified earlier in this article. This can actually help prevent your account from falling into a negative balance.
In particular I've made the interface for beginning a new backtest a lot simpler by encapsulating a lot of the "boilerplate" code into a new Backtest class. I've also modified the system to be fully workable with multiple currency pairs. In this article I'll describe the new interface and show the usual Moving Average Crossover example on both GBP/USD and EUR/USD.
In particular I would like to make the system a lot faster, since it will allow parameter searches to be carried out in a reasonable time. While Python is a great tool, it's one drawback is that it is relatively slow when compared to C/C++. Hence I will be carrying out a lot of profiling to try and improve the execution speed of both the backtest and the performance calculations.
Margin is one of the most important concepts of Forex trading. However, a lot of people don't understand its significance, or simply misunderstand the term. A Forex margin is basically a good faith deposit that is needed to maintain open positions. A margin is not a fee or a transaction cost, but instead, a portion of your account equity set aside and assigned as a margin deposit.

As we've already stated, trading on margin is trading on money borrowed from your broker. Each time you open a trade on margin, your broker automatically allocates the required margin from your existing funds in the trading account in order to back the margin trade. The precise amount of allocated funds depends on the leverage ratio used on your account.
Margin requirements for futures and futures options are established by each exchange through a calculation algorithm known as SPAN margining. SPAN (Standard Portfolio Analysis of Risk) evaluates overall portfolio risk by calculating the worst possible loss that a portfolio of derivative and physical instruments might reasonably incur over a specified time period (typically one trading day.) This is done by computing the gains and losses that the portfolio would incur under different market conditions. The most important part of the SPAN methodology is the SPAN risk array, a set of numeric values that indicate how a particular contract will gain or lose value under various conditions. Each condition is called a risk scenario. The numeric value for each risk scenario represents the gain or loss that that particular contract will experience for a particular combination of price (or underlying price) change, volatility change, and decrease in time to expiration.

Free Margin – Your free margin represents your total equity minus any margin used for leveraged trades. For example, if your equity is $1,000 and your used margin is $100, your free margin would amount to $900. Following your free margin is extremely important, as it is used to withstand negative price fluctuations from your open trades and to open new leveraged trades. It’s important to understand that your free margin increases with profitable positions, but decreases with your losing positions. Once the free margin drops to zero or below, your broker will activate the so-called margin call and close all your open positions at the current market rate, in order to prevent your equity from falling below the required margin.
We use real-time margining to allow you to see your trading risk at any moment of the day. Our real-time margin system applies margin requirements throughout the day to new trades and trades already on the books and enforces initial margin requirements at the end of the day, with real-time liquidation of positions instead of delayed margin calls. This system allows us to maintain our low commissions because we do not have to spread the cost of credit losses to customers in the form of higher costs.

The market values/prices used to compute the equity or margin requirement in an Interactive account may differ from the price disseminated by exchanges or other market data sources, and may represent Interactive's valuation of the product. Among other things, Interactive may calculate its own index values, Exchange Traded Fund values or derivatives values, and Interactive may value securities or futures or other investment products based on bid price, offer price, last sale price, midpoint or using some other method. Interactive may use a valuation methodology that is more conservative than the marketplace as a whole.
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