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2. Buying equals selling

Every purchase of the base currency implies a reciprocal sale of the secondary currency. Likewise, sale of the base currency implies the simultaneous purchase of the secondary currency.

For example, when I sell 1 GBP, I am simultaneously buying 1.5545 USD. Likewise, when I buy 1 GBP, I am simultaneously selling 1.5550 USD.

We can express this equivalence by inverting the GBP/USD exchange rate and rotating the bid and offer reciprocals, to derive the USD/GBP rate i.e.

USD/GBP = (1/1.5550) bid; (1/1.5545) offer = 0.6431/33

This means that the bid price of one USD is 0.6431 GBP (or 64.31p) and the offer price of one USD is 0.6433 GBP (or 64.33p). Note that USD has now become the base currency and that the spread is 2 points.

3. Practical spot trading

3.1 Units of trading – lots

As we have already seen, every forex transaction is an exchange of one currency for another. The basic unit of trading for private investors is known as a “lot” which consists of 100,000 units of the base currency (although some brokers may arrange trading in mini-lots).

• Using the data in Table A, the purchase of a single lot of GBP/USD will involve the purchase of 100,000 GBP at a price of 1.5852 USD = 158,520 USD.
• Similarly, the sale of a single lot of GBP/USD entails the sale of 100,000 GBP at 1.5847 USD = 158,470 USD.

3.2 Margin

A private investor who purchases a GBP/USD lot does not have to put down the full value of the trade (158,520 USD). Instead, the buyer is required to put down a deposit known as “margin” which enables the investor to gear up the trade size to institutional level.

Since the sale of one currency involves the simultaneous purchase of another, the seller of a GBP/USD lot will have bought a volume of USD, and will also have to put down margin for the value of the deal (158,470 USD).

The normal margin requirement is between 1% and 5% of the underlying value of the trade. The currency denomination depends on the brokerage through which you execute your trade. If you are dealing through an American broker (say online), then it is likely that you will have to deposit margin in USD even if you are resident in the UK.

With 5,000 USD in your margin account and with margin requirement of 2.5%, you can open positions worth 200,000 USD. Your positions will be valued continuously. If the funds in your margin account drop below the minimum required to support your open positions, then you may be asked to provide additional funds. This is known as a “margin call”.

If your trade is denominated in a currency other than that accepted by the broker, you will have to convert your gains and losses back into an acceptable currency. For example, if you trade a USD/JPY pair, then your gains and losses will be denominated in JPY. If your broker’s home currency is USD, then your profits and losses will be converted back to USD at the relevant USD/JPY offer rate.

3.3 Going short – going long

When you buy a currency, you are said to be “long” in that currency. Long positions are entered into at the offer price. Thus if you are buying one GBP/USD lot quoted at 1.5847/52, then you will buy 100,000 GBP at 1.5852 USD.

When you sell a currency, you are said to be “short” in that currency. Short positions are entered into at the bid price, which is 1.5847 USD in our example.

Because of the symmetry of currency transactions, you are always simultaneously long in one currency and short in another. For example if you exchange 100,000 GBP for USD you are short in sterling and long in US dollars.

3.4 Closing out

An open position is one that is live and ongoing. As long as the position is open, its value will fluctuate in accordance with the exchange rate in the market. Any profits and losses will exist on paper only and will be reflected in your margin account.

To close out your position, you conduct an equal and opposite trade in the same currency pair. For example, if you have gone long in one lot of GBP/USD (at the prevailing offer price) you can close out that position by subsequently going short in one GBP/USD lot (at the prevailing bid price).

Your opening and closing trades must the conducted through the same intermediary. You cannot open a GBP/USD position with Broker A and close it out through Broker B.