Overnight index swaps, or OIS, are derivatives that let markets express views on the average overnight policy-related rate over a future period. Desks treat OIS curves as a clean-ish map of rate expectations — complementary to, but not identical with, futures-based tools such as CME FedWatch.
This is tooling literacy for UK beginners, not a swaps primer for the dealing room. For the futures-probability tool, see how FedWatch probabilities work. Here we stay with OIS.
The basic idea
In an OIS, one side pays a fixed rate and the other pays a floating rate linked to a compounded overnight index — for example a policy-linked overnight rate in that currency. The fixed rate that makes the contract fair is tightly connected to what the market expects overnight rates to average over the term. When expected policy easing increases, relevant OIS rates tend to fall; when expected tightening increases, they tend to rise.
Samuel & Co Trading’s assessment is that beginners need that intuition — OIS as expectation plumbing — before any spreadsheet. The formula can wait; the habit of reading the priced path cannot.
Why desks use it
OIS is closely tied to expected overnight policy rates and is widely used in pricing and risk. It is often discussed as having less credit-spread contamination than some older interbank reference frameworks, though no instrument is philosophy-pure. For macro traders the practical win is a curve of implied policy paths across horizons: the next meeting, the next year, several years out.
FedWatch transforms fed funds futures into probabilities of hike or cut ranges for specific FOMC dates. OIS gives a curve of fixed rates linked to overnight expectations across tenors. Both speak to the path; they can diverge slightly because of instrument design, timing, convexity and liquidity. Small gaps are not a reason to panic. Large gaps deserve a second look at what each tool is actually quoting.
How the language lands
You will hear “OIS is pricing two cuts by December” or “the cut is fully priced in OIS.” That is shorthand for extracting meeting-by-meeting or cumulative easing from the curve. The extraction has assumptions. Treat media shorthand as a headline, then verify with a primary curve chart when the decision matters to your framework.
Relative OIS paths between the US and the euro area — or the UK — feed differential-rate stories in EUR/USD and cable. When ECB OIS eases faster than Fed OIS, rate support for the euro can weaken, all else equal. Cross-currency basis and risk sentiment still interfere; OIS is necessary context, not a full FX model.
Pitfalls
“Priced” is not “will happen.” Pricing is a probability-weighted market view, constantly revised. Do not mix spot overnight rates with forward OIS tenors. Liquidity and year-end effects can twist short tenors. Long tenors embed more than pure expected overnight averages — they are not a precision read on the terminal “neutral” rate.
OIS is not a guarantee of what the central bank will do. Risk premia, liquidity and positioning affect levels. A curve can look certain about cuts the committee never delivers if inflation re-accelerates. Treat OIS as the market’s working assumption, then listen to the committee’s own words — statements, projections and hawkish versus dovish tone.
UK angle
Sterling traders can watch SONIA-linked OIS for Bank of England path pricing alongside gilt moves. Euro and dollar OIS matter when rate differentials drive EUR/USD or cable. You do not need a swaps account to benefit from reading the priced path before UK or US data.
Before a meeting, note what OIS — or your broker’s rate-expectation readout — implies for the next few meetings. After the decision and press conference, see whether the curve’s change matches the narrative you heard. Divergences — dovish words but stubbornly high OIS — are educational signals that something in the package did not convince.
OIS contracts encode market expectations of overnight policy-related rates across horizons. UK beginners should use them as path-expectation plumbing alongside futures odds tools — remembering that priced is not promised, and that FX cares about relative OIS paths, not one curve in isolation.
If you want a structured read on whether your process is ready to sit through rate-path weeks without chasing every headline, take the free traders assessment at assessment.samuelandcotrading.com.
