Plain definition
Cost of capital is the return that lenders and owners require for committing money to a business. It reflects what they could earn elsewhere and the risk, timing, currency, and liquidity of the funds they provide. Management uses it as a hurdle or as an input to a discount rate when it compares investments.
It is not simply the interest rate on the newest loan. Equity holders also require a return, and the relevant rate can differ when a project has a different risk from the established business. A stable replacement asset and an untested launch may therefore need different assessments even when the company funds both from the same bank account.
Illustrative example
Suppose a company can either replace a proven production machine or enter an unfamiliar market. The replacement has known demand and an operating history; the launch depends on a new customer segment and a new distributor. Applying one company-wide return requirement without explaining that risk difference can make the launch appear safer than it is, or make the replacement appear less attractive than it is.
The useful discussion is not a search for a precise universal percentage. It is whether the expected cash flows, their uncertainty, and the return demanded by the providers of funds have been matched on a consistent basis.
A cost of capital is a decision assumption supported by evidence and judgment. It does not turn an implausible sales forecast into a reliable investment.
Why it matters
It connects a project to the real cost of tying up capital. Without it, a project can look attractive merely because it earns a positive accounting profit, even though it does not compensate the people who supplied the money or leaves the business short of cash for a better use.
Practical consequence
State whose return requirement the rate represents and why it fits the project’s currency, timing, inflation basis, and risk. Separate risks already reduced in the cash forecast from risks still present in it, so they are not counted twice. Show a defensible range and identify which assumption would need evidence before management accepted the lower end of that range.