The accounting equation: the one formula everything rests on

Every set of books ever kept obeys a single equation, and once you see it, the whole system stops feeling arbitrary:

Assets = Liabilities + Equity

In plain terms: everything a business owns was paid for either with money it owes or money that belongs to the owners. There’s no third source. A $10,000 van is either partly a loan, partly the owner’s stake, or some mix — but the two sides always add up to the same number.

Why it can never go out of balance

This is why accounting is double-entry. Every transaction keeps both sides equal. Buy the van with a loan: assets +$10,000, liabilities +$10,000 — balanced. Pay a bill from the bank: cash (asset) down, payables (liability) down — balanced. If your books don’t balance, the equation is telling you a transaction got recorded on one side only.

The expanded version

Equity isn’t static — it grows and shrinks with the business:

Assets = Liabilities + (Capital + Income − Expenses − Withdrawals)

Income increases equity; expenses decrease it. That’s why income and expense accounts behave the way they do, and why a year’s profit flows into retained earnings.