Buy Rate, Sell Rate, and Spread — Pricing in a Currency Exchange

Every exchange bureau has two rates: the rate at which it buys and the rate at which it sells. The gap between the two is the spread — and that is where the entire operating profit of the exchange business comes from.

That simple, and that complicated. Because if the spread is too wide, the customer goes to the exchange next door; if it is too tight, one rate movement eats the whole margin and you lose money on the trade without even noticing.

Three rates, not two

Most exchange bureaus think in two rates: buy and sell. But in reality, three rates are involved:

• Buy rate: The price at which you buy currency from the customer (lower).
• Sell rate: The price at which you sell to the customer (higher).
• Reference rate (mid-rate): The real market price at that moment — the point around which buying and selling rotate.

The reference rate is invisible, but it is the most important one. Because:

Your profit comes from the distance between your buy/sell rates and the reference rate, not from the posted rate of the exchange bureau across the street.

If you do not know the reference rate, you are pricing in the dark. You may think you are making money while the market has moved under your feet and your sell rate is now below the reference rate — meaning you are losing money on every trade.

How do we calculate spread?

Spread is expressed in two ways, and mixing them up is dangerous:

1. Absolute spread: The raw difference between the two rates.

Sell rate − buy rate = spread

Example: You buy dirham at 15,000 and sell at 15,150 → absolute spread = 150 rials per dirham.

2. Percentage spread: The same difference, relative to the reference rate.

(Absolute spread ÷ reference rate) × 100

If the reference rate is 15,075: (150 ÷ 15,075) × 100 ≈ 1%.

Why does percentage matter? Because absolute spread is not comparable across currencies. 150 rials on dirham means 1%, but 150 rials on dollar (which is 60,000) means 0.25%. If you only look at the absolute number, you think the spread is the same on both — while on dollar you are working almost for free.

Rule: always think about spread as a percentage, and quote it as an absolute number.

What determines the spread?

Spread is not a fixed number; it depends on several things:

• Currency volatility: A volatile currency (whose rate can move a lot by tomorrow) needs a wider spread, because holding it carries more risk. A stable currency can have a tighter spread.
• Liquidity: A currency you can easily buy and sell (dollar, dirham) has a lower spread. A thinly traded currency has a higher one — because it may sit in your inventory for a while.
• Transaction size: A wholesale customer usually gets a better spread. That is a volume discount, not weakness.
• Local competition: If there are ten exchange bureaus on one street, spreads move closer together. Differentiation comes from somewhere else (speed, trust, service).
• Your position direction: If you have a large dirham balance and want to reduce it, you make your sell rate slightly more attractive so you can sell faster. Spread is also a position management tool, not just a source of profit.

The big trap: nominal spread versus real spread

This is where many exchange bureaus quietly lose money.

Assume you set a 1% spread and think you are making 1% profit on every trade. But that 1% is the nominal spread — the distance between your buy and sell rates. The real spread is something else:

Your sell rate − the actual average cost of your inventory

If the market has risen since you bought, your average inventory cost is lower than today’s reference rate and your real spread is more than 1% (luck was on your side). But if the market has fallen, your average inventory cost is higher than the reference rate and your real spread can become negative — meaning that even though you are selling above today’s buy rate, you are selling below your average inventory cost and losing money.

Nominal spread tells you how much profit you hope to make; real spread tells you how much you actually made. And the gap between them is the volatility sitting on your open inventory.

That is why proper pricing is impossible without knowing the average cost of inventory. Setting rates blind to cost, sooner or later, ends in selling below cost.

Where do we get the reference rate?

The reference rate must be:

• Live: The FX market moves by the minute. A reference rate from two hours ago is not a reference rate.
• Reliable: From a source that actually reflects the market, not a manual number someone entered in the morning and forgot to update.
• Available for all currencies: Not just dollar — dirham, lira, yuan, euro, and anything else you trade.

Then build buy and sell rates around this reference rate, with the target spread for each currency, automatically. Doing this manually, on a busy day, is exactly where errors enter: one zero is missed, one currency is not updated, and you trade for hours at the wrong rate.

In Nexto, the live reference rate (with the source shown) is the base; each currency’s buy and sell rates are built around it with configurable spread, and because the system knows the average inventory cost, it can warn you when your sell rate gets close to your average inventory cost — before you lose money, not after.

Summary

Spread is the profit engine of an exchange bureau, but an engine that burns you if it is tuned blindly. Keep three things separate: the reference rate (market reality), nominal spread (the gap between your rates), and real spread (the distance to your average inventory cost). Think about price in percentage terms, be sensitive to the volatility and liquidity of each currency, and never set rates without knowing the actual cost.

Want to see how live rates and automatic spread work in practice? Build a dedicated demo and price a few currencies with different spreads.