What it means
Every banking day ends with a mismatch, as some banks hold more reserves than they need, others fall short, and the overnight market is where the two sides meet before tomorrow. The rate from that market is the system's base note: central banks steer it as their main policy lever, and every other interest rate in the economy takes its cue from there.
The Bank of Canada calls its target the policy interest rate explicitly, and its published key-rate page shows the target for the overnight rate as the headline instrument of monetary policy. Mechanics differ by country but rhyme, with some central banks setting a corridor with deposit and lending facilities and others targeting the market rate through open market operations, and all aiming at the same overnight anchor.
Settlement systems make it tangible, since reserves move between banks over the central bank's own rails, so the overnight loan is a book entry at the monetary authority, not a wire across town. A quarter-point move travels far, because mortgages, business loans and deposit rates reprice within weeks of an overnight-rate change, which is why central-bank decisions anchor the financial calendar.
The one number set between banks each night ends up inside mortgage offers, savings yields and currency values across the whole economy. The market watches the gaps: when the traded overnight rate strays from the central bank's target, money-market desks read stress or excess liquidity before any official statement arrives.
Crisis tests the plumbing, as when trust between banks breaks the overnight market seizes first, and central banks learn the state of the system from its price before anywhere else. The meeting calendar disciplines the market too, because decisions cluster on announced dates, liquidity thins beforehand and the rate itself goes quiet, a stillness that breaks the moment the statement lands.
Benchmarks grew from the same soil, and reference rates built on overnight transactions, like the secured overnight financing rate, now underpin trillions in contracts that once leaned on older fixings. Derivatives bet on its path, since overnight index swaps let banks and companies lock the average of future overnight rates, and their pricing is the market's running forecast of policy.
For a treasurer, the rate is the cash price of time. Overnight deposits and short borrowings price off it directly, so the cash manager's daily yield moves with every policy meeting.
In practice
Real-world examples.
Example
The central bank raises its target by 25 basis points (0.25%). Bank prime rates follow within days, and a borrower's revolving facility reprices at the next reset. On a $4 million facility, the extra annual interest is $10,000 (0.25% x $4 million).
Example
The traded overnight rate drifts above target for a week. Analysts read reserve scarcity, and the central bank adds liquidity to pull it back. The gap closing is itself the signal that the stress has passed.
Example
A corporate locks its short-term borrowing cost with an overnight index swap. The floating leg now pays whatever the daily fixings average, and the budget stops guessing. The treasurer reports the locked cost to the board each quarter.
Formula
Calculation
Interest for one night = principal x rate / 360, by money-market convention. Effective annual cost at an overnight rate r compounded daily is roughly (1 + r/360)^360 - 1.
Worked example. At 5%, a $10,000,000 overnight placement earns $10,000,000 x 5% / 360 = about $1,389 for the night. Compounded daily over 360 days, the effective annual rate is (1 + 0.05/360)^360 - 1 = about 5.13%, so the placement would grow by roughly $512,700 against $500,000 of simple interest. If the rate is cut to 4.5%, the nightly interest falls to $10,000,000 x 4.5% / 360 = $1,250, a drop of about $139 a night ($1,389 - $1,250).Case study
Seen in the real world.
In this illustrative fictional case, Omar, treasurer of a mid-sized retailer, keeps $30 million in overnight deposits. When the central bank cuts by half a point over two meetings, his annual interest income falls by roughly $150,000 (0.5% x $30 million), and he ladders part of the cash into three-month paper to defend the yield. He keeps $10 million overnight for liquidity and spreads $20 million across three-month paper in three tranches, so that maturities roll monthly. If the paper yields 0.25% more than overnight deposits, the extra income on $20 million is $50,000 a year (0.25% x $20 million), which recovers a third of the $150,000 drop.
Watch out
Common mistakes.
- Confusing the target with the traded rate, when the central bank sets the target and the market trades around it, and the gap between the two is itself information about the system's stress.
- Treating one night's rate as trivial, when it anchors the entire curve, and a quarter point compounded across mortgages and loans moves billions in annual interest.
- Assuming the lever works instantly, when policy moves the overnight rate in a day but spending and hiring respond over quarters, and the lag shapes every central-bank decision.
Questions
People also ask.
What is the overnight rate?
The rate banks charge each other to borrow reserves for one night. Central banks target it as their main policy lever, and every other rate in the economy reprices from it. Canada publishes its target as the policy interest rate.
Why does it matter outside banking?
It is the base note for mortgages, business loans and deposit yields. A quarter-point move travels through the whole economy within weeks, which is why rate decisions anchor the financial calendar. Everything reprices from it.
What should a treasurer watch?
The target, the traded rate's gap from it, and the meeting calendar. Cash yields and short borrowing costs move with each decision, and the gap flags stress before statements do.
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