What it means
Prime is a reference rate rather than a market-traded rate. Each bank sets its own, but in practice they cluster tightly together and move within days of a central bank decision, because the underlying cost of funds moves for everyone at once.
The rate matters to businesses because so much everyday credit is tied to it: overdrafts, revolving credit facilities, equipment finance and many small business term loans. A one percentage point rise in prime therefore raises the interest cost on every one of those facilities simultaneously, with no renegotiation required.
The margin above prime is where the borrower's own credit quality shows up. A well-capitalised company with strong cash flow might borrow at prime plus 0.5%, while a young business with thin collateral might be quoted prime plus 4% or more for the same facility.
Because prime-linked debt is floating rate, interest cost becomes a variable that has to be forecast rather than a fixed line in the budget. Finance teams commonly model a base case, a plus-two-percent case and a minus-one-percent case to see how much headroom the business has if rates move.
The nuance worth knowing is that prime is not the lowest rate available anywhere. Large corporates often borrow more cheaply than prime by pricing off interbank benchmarks directly, so prime is really the reference for small and mid-sized commercial borrowers.
In practice
Real-world examples.
Example
A construction firm's $250,000 working capital line is priced at prime plus 2%. When the central bank raises rates twice in a year and prime climbs from 7.5% to 8.5%, the firm's annual interest on a fully drawn line rises by $2,500 without a single document being resigned.
Example
A bakery chain negotiates a reduction in its margin from prime plus 3.5% to prime plus 2.25% after two years of clean covenant compliance. The prime rate itself is unchanged, but the saving on its $400,000 average balance is $5,000 a year.
Example
A finance director comparing a fixed-rate term loan at 9% with a prime-linked facility currently costing 9.5% chooses the fixed option, judging that the certainty is worth the small starting premium given the direction of policy rates.
Think of it
“Prime rate is the best rate for top borrowers-the base for many loan rates.
Formula
Calculation
Borrower rate = prime rate + agreed margin, and annual interest = outstanding balance x borrower rate. Suppose the prime rate is 7.5% and a company's revolving facility is priced at prime plus 2%, giving a borrower rate of 7.5% + 2% = 9.5%. If the company draws the full $250,000 facility for a year, annual interest is 250,000 x 0.095 = $23,750. In practice the balance fluctuates, so if the average drawn balance for a given month is $180,000, that month's interest is 180,000 x 0.095 / 12 = $1,425. Should prime rise to 8.5%, the borrower rate becomes 10.5% and the full-facility annual cost rises to 250,000 x 0.105 = $26,250, an extra $2,500 a year.Case study
Seen in the real world.
Brightwater Print Group is an illustrative, fictional commercial printing business. It funded a plant expansion with a $250,000 revolving facility priced at prime plus 2%, budgeting interest at $23,750 a year based on a prime rate of 7.5%.
Over the following eighteen months prime rose by a full percentage point, taking the borrower rate to 10.5% and the annual cost on a fully drawn line to $26,250. The extra $2,500 was manageable on its own, but it landed in the same year as a paper price increase, and the combined effect pushed the company through a covenant threshold on interest cover.
In this fictional example the company renegotiated part of the balance onto a fixed rate and reduced its average drawn balance by tightening receivables collection. The illustrative point is that floating rate debt transfers rate risk to the borrower, and that risk needs a place in the forecast rather than a footnote.
Watch out
Common mistakes.
- Assuming the prime rate is set by the central bank. Central banks set policy rates, and commercial banks then set their own prime rate, which almost always moves in step but is a separate published number.
- Believing prime is the cheapest borrowing rate in the market. Large corporates frequently borrow below prime by pricing off interbank benchmarks, so prime is the reference point for smaller commercial borrowers rather than a floor.
- Budgeting prime-linked interest as a fixed annual cost. A prime-linked facility reprices automatically, so the interest line should be modelled across a range of rate scenarios.
Questions
People also ask.
What does "prime plus 2" actually mean?
It means the borrower pays the current prime rate plus two percentage points, so at a prime rate of 7.5% the borrower rate is 9.5%.
How often does the prime rate change?
It changes whenever banks respond to a shift in central bank policy, which in a stable period may be once or twice a year and in a volatile period several times.
Should a business prefer fixed or prime-linked borrowing?
It depends on rate outlook and risk appetite, but businesses with thin margins or tight covenants often pay a small premium for fixed rates to keep the interest line predictable.
From the founder's library
Take it further with the book.
Build your financial confidence beyond this definition. Shihan's full-length guide, Accounting Fundamentals, takes the same plain-English approach and turns it into a complete, practical playbook for non-finance managers, business owners and students - with chapter-end quiz answers and presentation slides included.
25% off with code MMHQ25, applied at checkout. Priced in USD - checkout may show the equivalent in your local currency.
View the book and save 25%Related