Double-entry bookkeeping is the foundation of all financial accounting. Every transaction in every accounting system in the world, from Bexio to SAP, is recorded using the same principle: each transaction affects at least two accounts, and the total of all debit entries always equals the total of all credit entries.

This principle is five centuries old and has not changed because it works. It creates a self-checking system: if debits and credits do not balance, something has been recorded incorrectly, and the imbalance reveals that a problem exists even before anyone identifies what it is.

For controllers, understanding double-entry at the transaction level, not just at the report level, is what enables them to diagnose reporting problems, review accrual entries with confidence, and understand why the balance sheet always balances regardless of what happens in the business. This article walks through the mechanics using a real business scenario from inception.

The Mechanics: Debits, Credits, and Account Types

Every account in the chart of accounts is either an asset, liability, equity, revenue, or expense account. The sign convention for debits and credits works differently depending on the account type, which is the source of most confusion for people first learning the system.

The T-account framework makes this visual. Every account can be represented as a T: the left side is the debit side, the right side is the credit side.

Asset accounts increase with debits and decrease with credits. Cash received increases the cash account: debit cash. Cash paid out decreases the cash account: credit cash.

Liability accounts increase with credits and decrease with debits. A new loan increases the loan payable account: credit loan payable. Repaying the loan decreases it: debit loan payable.

Equity accounts increase with credits and decrease with debits. A shareholder paying in capital increases equity: credit share capital. A loss reduces equity: debit retained earnings.

Revenue accounts increase with credits. Recognising a sale: credit revenue.

Expense accounts increase with debits. Recording a cost: debit expense account.

The governing rule is always: total debits equal total credits for every transaction. If you credit revenue (increase), you must debit something else, typically accounts receivable (increase) or cash (increase).

The Simulation: Helvetex Services AG, January 2025

Helvetex Services AG is a newly incorporated Swiss GmbH providing management consulting services. It begins operations in January 2025. We will trace the first eight transactions through the accounting system, showing the journal entry for each and the cumulative effect on the balance sheet and P&L.

Opening balance sheet before any transactions: zero everything. No assets, no liabilities, no equity.

Transaction 1: Shareholder invests CHF 50,000 as initial capital.

The company receives CHF 50,000 in its bank account. Equity increases by CHF 50,000.

Debit: Bank account (asset +) CHF 50,000 Credit: Share capital (equity +) CHF 50,000

Balance sheet after transaction 1: Assets: Bank CHF 50,000 Equity: Share capital CHF 50,000 Everything balances.

Transaction 2: Company pays three months’ office rent in advance, CHF 6,000 (CHF 2,000 per month).

Cash decreases. A prepaid expense asset is created (the right to use the office for three months, which has not yet been consumed).

Debit: Prepaid rent (asset +) CHF 6,000 Credit: Bank account (asset -) CHF 6,000

Balance sheet after transaction 2: Assets: Bank CHF 44,000, Prepaid rent CHF 6,000 = Total assets CHF 50,000 Equity: Share capital CHF 50,000 Still balanced.

Transaction 3: Company purchases a laptop for CHF 2,400 cash.

Cash decreases. A fixed asset is created.

Debit: Equipment (asset +) CHF 2,400 Credit: Bank account (asset -) CHF 2,400

Balance sheet after transaction 3: Assets: Bank CHF 41,600, Prepaid rent CHF 6,000, Equipment CHF 2,400 = Total CHF 50,000 Equity: Share capital CHF 50,000

Transaction 4: Company invoices a client CHF 12,000 for consulting work completed in January.

Revenue is recognised (the work has been done). A receivable is created (the client owes money).

Debit: Accounts receivable (asset +) CHF 12,000 Credit: Revenue (income +) CHF 12,000

Balance sheet after transaction 4: Assets: Bank CHF 41,600, Receivables CHF 12,000, Prepaid rent CHF 6,000, Equipment CHF 2,400 = Total CHF 62,000 Equity: Share capital CHF 50,000, Retained earnings (profit) CHF 12,000 = Total CHF 62,000

The P&L so far: Revenue CHF 12,000. Profit CHF 12,000.

Transaction 5: Company receives the CHF 12,000 payment from the client.

The receivable is settled. Cash increases. The receivable disappears.

Debit: Bank account (asset +) CHF 12,000 Credit: Accounts receivable (asset -) CHF 12,000

Balance sheet after transaction 5: Assets: Bank CHF 53,600, Prepaid rent CHF 6,000, Equipment CHF 2,400 = Total CHF 62,000 Equity: CHF 62,000 The P&L is unchanged - revenue was already recognised in transaction 4.

This is the transaction that illustrates the difference between profit and cash discussed in article 15. The profit was recorded in January when the work was done (transaction 4). The cash arrived later (transaction 5). Both are correctly recorded. The timing difference is visible in the sequence.

Transaction 6: Month-end accrual for January rent, CHF 2,000.

One month of the prepaid rent has been consumed. The asset is reduced; the expense is recognised.

Debit: Rent expense (expense +) CHF 2,000 Credit: Prepaid rent (asset -) CHF 2,000

Balance sheet after transaction 6: Assets: Bank CHF 53,600, Prepaid rent CHF 4,000, Equipment CHF 2,400 = Total CHF 60,000 Equity: Share capital CHF 50,000, Retained earnings CHF 10,000 = Total CHF 60,000

P&L so far: Revenue CHF 12,000 minus Rent expense CHF 2,000 = Profit CHF 10,000.

Transaction 7: Month-end depreciation on laptop, CHF 40 (CHF 2,400 over 60 months).

The laptop is being consumed over its useful life. The asset value decreases; a depreciation expense is recognised.

Debit: Depreciation expense (expense +) CHF 40 Credit: Accumulated depreciation (contra-asset -) CHF 40

Balance sheet after transaction 7: Assets: Bank CHF 53,600, Prepaid rent CHF 4,000, Equipment net of depreciation CHF 2,360 = Total CHF 59,960 Equity: Share capital CHF 50,000, Retained earnings CHF 9,960 = Total CHF 59,960

P&L: Revenue CHF 12,000 minus Rent CHF 2,000 minus Depreciation CHF 40 = Profit CHF 9,960.

This entry illustrates why depreciation is a non-cash expense: no cash moved in transaction 7. The cash moved in transaction 3 when the laptop was purchased. The P&L spreads the cost over the asset’s life; the cash was already gone.

Transaction 8: Company receives a supplier invoice for CHF 800 for software subscriptions, not yet paid.

An expense is incurred and recognised. A payable is created.

Debit: Software expense (expense +) CHF 800 Credit: Accounts payable (liability +) CHF 800

Balance sheet after transaction 8: Assets: Bank CHF 53,600, Prepaid rent CHF 4,000, Equipment net CHF 2,360 = Total CHF 59,960 Liabilities: Accounts payable CHF 800 Equity: Share capital CHF 50,000, Retained earnings CHF 9,160 = Total CHF 59,960

P&L: Revenue CHF 12,000 minus Rent CHF 2,000 minus Depreciation CHF 40 minus Software CHF 800 = Profit CHF 9,160.

What the Simulation Reveals

Eight transactions in, and the simulation has illustrated the key principles that underpin all of financial accounting.

The balance sheet always balances because every transaction has equal and opposite effects. This is not a coincidence or a target. It is mathematically guaranteed by the structure of double-entry.

Profit and cash are different things. Transaction 4 created profit. Transaction 5 created cash. The timing difference between the two is working capital.

Accruals match expenses to the period in which they are incurred, not the period in which cash moves. Transactions 6, 7, and 8 all create expenses without moving cash.

Assets are consumed over time, not expensed all at once. Transaction 7 shows the mechanism: depreciation matches the economic consumption of the asset to the periods that benefit from it.

Understanding these mechanics at the transaction level is what allows a controller to review a trial balance, identify unusual entries, and diagnose reporting problems that are invisible if you only ever look at the P&L.

Looking for professional, Swiss-context Excel templates? Browse the template library or book a free call.

Alessandro Ratzenberger is a fractional CFO and business controller based in Zurich, with 15 years of operational finance experience at Dufry Group and Bomi (UPS Group).