Your general ledger tells you that customers owe you £18,400. Your subledger tells you which customers, for which invoices, and how overdue each one is. Get them to agree every month and your books are trustworthy. Let them drift apart and you are filing accounts on numbers you cannot stand behind.
If you have ever opened Xero or QuickBooks and wondered why there is both a single "Accounts Receivable" line in your reports and a separate, detailed list of every unpaid customer invoice, you have already met the two layers of bookkeeping this guide explains. One is the general ledger. The other is the subledger. They are not duplicates — they are designed to check each other.
What the general ledger actually is
The general ledger (GL) is the master record of your business. Every transaction your business makes ends up summarised here, sorted into accounts: sales, bank, VAT, wages, rent, and so on. It is the single source of truth that your trial balance is built from, and the trial balance in turn feeds your profit and loss and balance sheet.
Think of the GL as the index at the front of a book. It tells you the totals — total owed by customers, total owed to suppliers, total in the bank — but it does not, on its own, tell you the line-by-line detail behind each figure. That detail lives one level down, in the subledgers.
Why the GL is kept summarised
If every individual customer invoice were posted directly into the general ledger as its own account, the GL would have thousands of lines and the trial balance would be unreadable. So the GL holds a single summary figure for each category, and the granular detail is held separately and rolled up. That summary figure in the GL is called a control account.
What a subledger is
A subledger (also called a subsidiary ledger) is the detailed breakdown that sits behind one control account in the general ledger. It records every individual transaction that makes up that control total. The four most common subledgers in a UK small business are:
- Accounts receivable (sales/debtors ledger) — every unpaid customer invoice, by customer.
- Accounts payable (purchase/creditors ledger) — every unpaid supplier bill, by supplier.
- Fixed assets — every asset you own, its cost, and accumulated depreciation.
- Inventory (stock) — every product line, quantity and value held.
The golden rule: the sum of all the lines in a subledger must equal the balance of its matching control account in the general ledger. If your AR subledger lists invoices totalling £18,400, the AR control account in the GL must read £18,400 too. Not £18,390. Not £18,410. Exactly £18,400.
What a control account does
A control account is the bridge between the two layers. It is a single account in the general ledger that "controls" — i.e. summarises — an entire subledger. The accounts receivable control account is the total of every customer balance. The accounts payable control account is the total of every supplier balance.
The point of a control account is verification. Because the subledger and the control account are maintained from the same source transactions but totalled independently, comparing the two is a built-in error check. When they match, you have strong evidence your debtor or creditor figures are right. When they do not, you know — before the numbers reach your accounts — that something is wrong.
How the posting flow works
In a manual system you would post each invoice twice: once to the customer's account in the subledger, and once (in summary) to the control account in the GL. In modern cloud software the double posting happens automatically the moment you raise or pay an invoice, so you rarely see the mechanics. But understanding the flow is what lets you fix things when they break.
Raising a sales invoice
When you issue an invoice to a customer, the software does two things at once:
- It adds the invoice to that customer's record in the AR subledger.
- It posts a summary entry to the GL: debit the AR control account, credit sales (and credit the VAT control account if you are VAT-registered).
Receiving a payment
When the customer pays, the software reduces that customer's balance in the subledger and posts a GL entry: debit bank, credit the AR control account. Both layers move together, which is exactly why they should stay in step. If you want a refresher on the related bank side of this, see our guide to bank reconciliation for small businesses.
A worked example: the AR subledger and its control account
Suppose your accounts receivable subledger at month-end shows three outstanding customer invoices:
- Acme Joinery Ltd — invoice 1042 — £7,200
- Brightline Cafés — invoice 1043 — £4,500
- Compass Logistics — invoice 1044 — £6,700
Add those up: £7,200 + £4,500 + £6,700 = £18,400. That is the total your customers owe you, according to the detailed subledger.
Now look at the AR control account in your general ledger. If it also shows £18,400, your receivables reconcile. The detail agrees with the summary, and you can sign off your debtors figure with confidence.
When the figures do not match
Now imagine the GL control account reads £18,900 — £500 more than the subledger. That £500 gap is a flag, not a footnote. Something has hit the control account that never made it onto a customer's record, or a payment was recorded against a customer but the GL entry was missed. Common causes:
- A manual journal posted straight to the AR control account, bypassing the subledger entirely.
- A customer credit note applied in the subledger but not posted to the GL.
- A receipt allocated to the wrong account, so the control account never reduced.
- An opening balance entered directly into the control account during a software migration.
The discipline is to chase the difference until it is zero. You are not "rounding it away" — a £500 mismatch could be a £6,700 invoice double-counted and a £6,200 one missing, netting to £500 but hiding two errors. Reconciling forces you to find both.
Why reconciliation is a month-end discipline
Subledger-to-GL reconciliation is one of the core month-end checks, alongside the bank rec. Doing it monthly keeps errors small and recent, so they are easy to trace. Leave it until year-end and you are unpicking twelve months of mismatches at once — usually the week your accounts are due.
For a limited company this matters legally as well as practically. You must keep accounting records that show and explain your company's transactions, including what the company owns and what it owes. Reliable debtor and creditor figures depend directly on subledgers that reconcile to the GL. Those records ultimately support the decisions and paperwork you build on top of them, from dividend declarations to your annual accounts.
What to reconcile each month
- AR control vs sales ledger — total of unpaid customer invoices.
- AP control vs purchase ledger — total of unpaid supplier bills.
- VAT control — agrees to your VAT return workings.
- Bank — GL bank balance agrees to the actual statement.
- Inventory / fixed assets — where you hold them, agree the register to the GL.
How this looks in Xero and QuickBooks
You will rarely post to a control account by hand in cloud software — and that is deliberate. In Xero, the Aged Receivables and Aged Payables reports are effectively your subledgers; the figures on the balance sheet are the control accounts. Run the Aged Receivables Summary at a date and compare its total to the Accounts Receivable line on the balance sheet at the same date. They should match to the penny.
QuickBooks works the same way: the A/R Ageing Summary should equal the Accounts Receivable balance on the balance sheet. When they diverge, the usual culprit is a manual journal posted directly to a system account or a transaction dated outside the reporting range. Keeping a tidy structure — see our note on building a sensible chart of accounts — makes these reconciliations far quicker. If you sell across marketplaces, the same logic underpins reconciling ecommerce payouts, where clearing accounts behave like mini control accounts.
Subledger vs general ledger: the quick comparison
At a glance, the general ledger holds the summarised totals and the subledger holds the line-by-line detail behind each one. The two are linked by a control account, and the test of a healthy ledger is that they reconcile to the penny every month:
| Feature | General ledger (GL) | Subledger |
|---|---|---|
| What it holds | Master record, summarised by account | Supporting detail, line by line |
| Level of detail | One control account per category | Every customer, supplier, asset or product |
| Feeds | Trial balance, profit and loss, balance sheet | Rolls up into its matching control account |
| Example total | AR control account: £18,400 | Three customer invoices summing to £18,400 |
| The test | Subledger total must equal its control account balance; reconcile monthly and investigate any difference | |
Common mistakes to avoid
- Posting journals to a control account. Doing so bypasses the subledger and guarantees a mismatch. Always raise an invoice, bill or credit note instead.
- Ignoring small differences. A small net figure can hide two large offsetting errors.
- Reconciling only at year-end. Twelve months of drift is far harder to unpick than one.
- Migrating opening balances carelessly. When moving software, load debtors and creditors as individual invoices, not a lump sum to the control account.
The bottom line
The general ledger gives you the headline totals; the subledgers give you the detail behind them; and control accounts are the hinge that lets you prove the two agree. Treat the subledger-to-GL reconciliation as a non-negotiable month-end task and your financial statements will rest on numbers you can defend — to your accountant, to HMRC, and to yourself.
Frequently asked questions
What is the difference between a subledger and the general ledger?
The general ledger is the master record holding a single summary balance for each category, such as accounts receivable. A subledger is the detailed breakdown behind one of those balances — for example, every individual unpaid customer invoice. The subledger total must always equal its control account balance in the general ledger.
What is a control account?
A control account is a single account in the general ledger that summarises an entire subledger, such as the accounts receivable control account totalling all customer balances. It exists as a built-in check: because the control account and the subledger are totalled independently, comparing them flags any error before the figures reach your financial statements.
Why won't my Xero or QuickBooks subledger match the general ledger?
The most common cause is a manual journal posted directly to a system control account, which bypasses the subledger. Other causes include credit notes applied in one layer but not the other, receipts allocated to the wrong account, or transactions dated outside your reporting range. Run the aged receivables or payables report and compare its total to the matching balance sheet line at the same date to locate the gap.
How often should I reconcile subledgers to the general ledger?
Monthly, as part of your month-end routine alongside the bank reconciliation. Reconciling every month keeps any errors small, recent and easy to trace, rather than leaving you to unpick a year of mismatches when your accounts are due.
