> ## Documentation Index
> Fetch the complete documentation index at: https://docs.lerian.studio/llms.txt
> Use this file to discover all available pages before exploring further.

# Revenue, expenses & costs

> What revenue is, what an expense is, and what a cost is — told apart in plain language. The two words that drive the Income Statement, and why the difference matters.

Two words show up everywhere in accounting: **revenue** and **expenses**. They're the money a business *earns* and the money it *spends*. Get these two straight and the [Income Statement](/en/fundamentals/accounting/financial-statements) — the report that says whether you made a profit — suddenly reads like a simple subtraction.

## Revenue — the money you earn

***

**Revenue** is the money a business earns from doing what it does: selling a product, providing a service, charging for a subscription. It's the top line — the reason the business exists in the first place.

Picture a bakery. Every loaf it sells brings in revenue. Add up a day's sales and that total is the day's revenue. It's the inflow that everything else gets measured against.

One thing to hold onto: revenue is about **what you earned**, not necessarily the cash sitting in your account today. That subtlety has its own page — [accrual vs. cash](/en/fundamentals/accounting/accrual-vs-cash) — but for now, just think of revenue as *money earned from the work*.

## Expenses — the money you spend to earn it

***

An **expense** is money the business spends to keep running and to earn that revenue: rent, salaries, electricity, flour for the bakery. If revenue is what comes in, expenses are what goes out to make it happen.

Expenses aren't a bad thing — they're the fuel. You can't sell bread without buying flour and paying the baker. The point of accounting isn't to avoid expenses; it's to know exactly what they are so you can tell whether the revenue was worth it.

## Cost — close to expense, but not identical

***

People use **cost** and **expense** as if they mean the same thing, and in casual talk they nearly do. The small distinction worth knowing:

* A **cost** is what you *pay* to get something — the price of acquiring a resource. Buying an oven for the bakery has a cost.
* An **expense** is a cost *counted against the revenue of a period* — the portion that's "used up" in earning this stretch's income. The flour baked into today's bread is an expense today.

In short: a **cost** becomes an **expense** once it's used up in the work of earning revenue. The oven is a cost when you buy it; the slice of its wear-and-tear that helped make this month's bread becomes an expense this month.

| Term        | Plain meaning                                | Bakery example                             |
| ----------- | -------------------------------------------- | ------------------------------------------ |
| **Revenue** | Money earned from the work                   | Selling loaves                             |
| **Cost**    | What you pay to acquire something            | Buying the oven                            |
| **Expense** | A cost used up to earn this period's revenue | The flour baked today, the rent this month |

Don't over-think the cost-versus-expense line — just know that "cost" leans toward *acquiring*, and "expense" leans toward *using up to earn revenue*. Follow one bag of flour through the bakery and the whole chain falls into place:

```mermaid theme={null}
flowchart LR
    A["Buy flour<br/><b>cost</b>"]:::cost --> B["Bake the bread<br/><b>expense</b>"]:::expense
    B --> C["Sell the bread<br/><b>revenue</b>"]:::revenue
    C --> D["Revenue − expenses<br/><b>profit or loss</b>"]:::profit
    classDef cost fill:#fef9c3,stroke:#ca8a04,color:#713f12
    classDef expense fill:#fed7aa,stroke:#ea580c,color:#7c2d12
    classDef revenue fill:#dbeafe,stroke:#2563eb,color:#1e3a8a
    classDef profit fill:#dcfce7,stroke:#16a34a,color:#14532d
```

## Why they matter to the Income Statement

***

These two words are the entire engine of the [Income Statement](/en/fundamentals/accounting/financial-statements):

* Start with **revenue** — the money earned.
* Subtract **expenses** — the money spent earning it.
* What's left is **profit** (or, if expenses were bigger, a **loss**).

A month at the bakery, in one line:

$$
\underbrace{\$1{,}000}_{revenue} - \underbrace{\$700}_{expenses} = \underbrace{\$300}_{profit}
$$

That's it. Revenue minus expenses tells you whether the business actually made money over a period. Every other line on the statement is just a more detailed way of grouping those two ideas.

And that profit doesn't just disappear — it flows into **equity**. Earn a profit and the owners' stake in the business grows; run a loss and it shrinks. That's the quiet link back to [Assets, liabilities & equity](/en/fundamentals/accounting/assets-liabilities-equity): the Income Statement is the story of *how* equity changed over a period.

## In short

***

* **Revenue** is the money a business earns from its work; **expenses** are the money it spends to earn that revenue.
* A **cost** is what you pay to acquire something; it becomes an **expense** once it's used up in earning a period's revenue.
* The **Income Statement** is simply **revenue minus expenses** — the difference is your profit or loss.

<Note>
  **Next up**

  Now you know the five account families. Next, see how every change to them gets written down — as [Debits and credits](/en/fundamentals/accounting/debits-and-credits).
</Note>