The real cost of one lot: spread, commission and swap
Ask a trader what a lot costs and most will quote the spread. The spread is one of three components, and on a position held for more than a few hours it is often not the largest.
The three components
Spread is the gap between the buy and sell price at the moment you enter. You pay it once, on entry, and it is charged whether the trade goes on to win or lose.
Commission is a separate charge on accounts that advertise a raw or zero spread. Instead of widening the price, the broker bills a flat amount per lot. Some brokers quote it per side, some per round turn, and the difference between those two readings is a factor of two.
Swap is the financing charge for holding a position overnight. It is applied each night the position stays open, it can be positive or negative depending on direction, and it is the component most often left out of a cost comparison because it does not appear until the day after.
A fourth number sits alongside them and moves in the opposite direction: the rebate, which comes back per lot after the trade closes.
Why quoting the spread alone misleads
The three components respond to different things.
Spread scales with the instrument and the session. Commission scales with lots and nothing else. Swap scales with how long you hold and does not care about your entry price at all.
So the ranking of two accounts changes with the shape of your trading, not just with the broker's price list. A scalper closing inside the hour pays spread and commission and never touches swap. A position trader holding a week pays swap over and over and barely notices a small spread difference.
| Component | Charged | Scales with |
|---|---|---|
| Spread | On entry | Instrument, session |
| Commission | Per lot | Volume only |
| Swap | Every night held | Holding time, direction |
| Rebate | After close | Volume |
Where the figures come from
Our [trading calculator](/tools/calculator) works out all four for a pair, an account type and a volume you enter, using spread measured from broker servers rather than from a marketing page.
Those measurements run every five minutes across the instruments we track, and a reading older than ten minutes is treated as stale rather than served as current. That matters for exactly the reason this article exists: a cost figure with no timestamp is a claim, not a measurement.
What to do with this
Work out your own number rather than borrowing one.
- Take the pair you actually trade, not the one with the best headline
- Enter the volume you traded last month, not a round figure
- Include swap if you hold overnight, and exclude it honestly if you do not
- Subtract the rebate last, because it applies to the total rather than to any single component
Every figure here moves. Read the live tables rather than any number written into an article, including this one.
Next
- [Why the advertised spread is not the spread you get](/bai-viet/advertised-vs-actual-spread)
- [What holding overnight actually costs](/bai-viet/what-swap-costs-you)