Subledger

A subledger (also written sub-ledger or subsidiary ledger) is a detailed set of records for one area of a business whose total feeds a single account in the general ledger. The receivables subledger, for example, lists every customer and every unpaid invoice; the general ledger shows only one line, "accounts receivable", whose balance should equal the subledger total.

Subledgers exist because the general ledger would be unreadable if it held every invoice, card payment and asset record. They keep detail where staff need it, for chasing a customer, paying a supplier or depreciating a machine, while the general ledger keeps the summary that feeds the financial statements. The link between the two is the control account, and keeping them in step is a core part of account reconciliation.

Picture a school office. The head teacher's notebook says "parents owe the school $12,000 in unpaid fees". That single line is enough for budgeting, but useless for chasing payment. So a clerk keeps a separate binder with one page per family, showing each bill and each payment.

The binder is the subledger and the head teacher's line is the control account in the general ledger. As long as the pages in the binder add up to $12,000, the two records agree. If they don't, someone has missed a payment or written something in only one place, and it has to be found.

Each subledger is tied to one or more general ledger control accounts. Postings flow one way: transactions are entered in the subledger, and the system posts a summary journal entry to the control account, either in real time or in batches. Staff are normally blocked from posting directly to a control account, because a direct posting would change the general ledger without changing the detail, and the two would no longer agree.

The check is simple:

Here $n$ is the number of customers, suppliers or items in the subledger and each subledger balance is one customer's, supplier's or item's balance. For example, if three customers owe $4,000, $5,000 and $3,000, the receivables control account should show $12,000. A difference points to a posting error, a timing difference or an unauthorised direct entry.

• Accounts receivable. Customer invoices, credit notes and receipts, used for collections and ageing; see accounts receivable and cash application.
• Accounts payable. Supplier invoices and payments, used to schedule payment runs; see accounts payable.
• Fixed assets. Each machine, vehicle or building with its cost, useful life and accumulated depreciation.
• Inventory. Quantities and costs by item and location.
• Payroll. Gross pay, deductions and net pay by employee, summarised to wage expense and payroll liabilities; see payroll and salary disbursement.
• Revenue or billing. Contracts, subscriptions and performance obligations used for revenue recognition.

In financial services, the largest subledger is usually the customer ledger. A bank's core banking system records each depositor's balance and each loan; the general ledger shows only total deposits and total loans. Card issuers keep a cardholder subledger, and acquirers keep a merchant subledger showing what each merchant is owed after fees.

Wallet providers and e-money firms follow the same pattern. The app's balance for each user is a subledger entry; the total of all user balances is a liability in the general ledger, and it must be matched by funds held in a safeguarding account or client money account. Regulators and auditors therefore look at three-way agreement: customer subledger, general ledger liability and bank balance. Engineering concerns such as ledger sharding, idempotency and balance caching mostly arise in this high-volume subledger layer, not in the general ledger.

Subledger-to-general-ledger reconciliation is a standard step in the financial close. Typical causes of differences include:

• Direct postings. A manual journal posted straight to a control account, bypassing the subledger.
• Cut-off timing. A batch posted to the subledger after the general ledger period was locked.
• Interface failures. A file between two systems that failed, partially loaded or loaded twice.
• Currency revaluation. Foreign-currency balances revalued at different rates in the two systems.

Where several systems are involved, firms often run multi-step reconciliation, matching transaction records first, then subledger totals, then the general ledger and finally the bank. Persistent unexplained differences are a warning sign for auditors, because they can hide errors or fraud.

• Internal Revenue Service: Recordkeeping