Subsidiary ledgers and control accounts, explained with practice

A business with three customers could keep one Accounts Receivable account and remember who owes what. A business with three hundred cannot. It needs to know, for each customer, what was billed, what was paid and what is still outstanding, so it can send statements, chase late payers and answer the question "how much do we owe you?" when a customer calls. The general ledger, though, should not have three hundred receivable accounts in it; the balance sheet needs a single figure.

The solution is a subsidiary ledger: a separate ledger with one account per customer (or per supplier), sitting behind a single control account in the general ledger. This page explains how the two fit together, works through a month of postings, and shows how to check that they agree.

How the pieces fit

• The accounts receivable subsidiary ledger (often called the customer ledger) has one account per customer. Each shows that customer's sales on account, payments and credit memos, and their balance.
• The accounts payable subsidiary ledger (the supplier or vendor ledger) has one account per supplier, showing purchases on account, payments and credit memos received.
• The control account is the single Accounts Receivable or Accounts Payable account in the general ledger. It receives the same transactions, usually in total, and it is the figure that goes into the trial balance and the balance sheet.

The rule that makes the system work: the balance of the control account must always equal the total of the balances in its subsidiary ledger. Every transaction that changes one must change the other by the same amount.

Other accounts can have subsidiary ledgers too, such as equipment (one record per asset) or inventory (one record per product), but receivables and payables are by far the most common, and they are what this lesson practises.

What gets posted where

The two "no effect" rows matter. A cash sale is settled on the spot, so the customer never owes anything and nothing is posted to Accounts Receivable or to any customer account. The same goes for purchases paid in cash. Our hardest exercises mix these in on purpose.

Worked example: a month of customer postings

Here is one of the practice problems. The business starts July with three customer balances:

The July transactions are:

1. July 5: Sold goods on account to Willow Dental, $1,060.00.
2. July 9: Kestrel Hotels returned goods sold on account; credit memo for $290.00.
3. July 13: Sold goods on account to Kestrel Hotels, $1,390.00.
4. July 17: Received $2,380.00 from Willow Dental in payment of its account.
5. July 21: Delta Fitness returned goods sold on account; credit memo for $545.00.
6. July 25: Received $235.00 from Willow Dental in payment of its account.

Step 1: post each customer's account

• Kestrel Hotels: $970.00 − $290.00 + $1,390.00 = $2,070.00.
• Delta Fitness: $1,820.00 − $545.00 = $1,275.00.
• Willow Dental: $1,585.00 + $1,060.00 − $2,380.00 − $235.00 = $30.00.

Step 2: update the control account

The control account starts at $4,375.00. Sales on account add $1,060.00 + $1,390.00 = $2,450.00. Returns subtract $290.00 + $545.00 = $835.00. Collections subtract $2,380.00 + $235.00 = $2,615.00. Ending balance: $4,375.00 + $2,450.00 − $835.00 − $2,615.00 = $3,375.00.

Step 3: reconcile

Add up the customer balances: $2,070.00 + $1,275.00 + $30.00 = $3,375.00. That matches the control account, so the postings agree. This list of customer balances with its total is called a schedule of accounts receivable (or, for suppliers, a schedule of accounts payable), and preparing it at each month end is a standard control.

Why the totals might not agree

When the schedule total and the control account differ, something was posted to one and not the other, or posted differently. The usual causes:

• A transaction was posted to the customer's account but not the control account, or the reverse.
• A credit memo was added to a customer's balance instead of subtracted.
• A cash sale was wrongly posted to a customer.
• A payment was posted to the wrong customer. This one does not show up in the totals, because the control account is still right; it shows up when the customer queries their statement.
• An arithmetic or transposition error in one customer's balance. As with trial balances, a difference that divides by 9 often points to a transposition (see finding and correcting errors).

In accounting software the control account is usually updated automatically from the customer and supplier records, so the two cannot drift apart through posting. But a manual journal entry made directly to Accounts Receivable or Accounts Payable, without a customer or supplier attached, can still break the link. That is one reason many bookkeepers lock the control accounts against manual entries.

The supplier side

Accounts payable works the same way with the directions flipped in the general ledger: purchases on account increase each supplier's balance and the Accounts Payable control account (a credit), while payments and supplier credit memos decrease them (a debit). The schedule of accounts payable lists each supplier's balance, and its total must equal the control account. Reconciling individual supplier accounts against the statements suppliers send is how missing invoices and duplicate payments are usually caught.

Using the customer ledger day to day

The subsidiary ledger is where most of the real work with customers and suppliers happens. A customer statement at month end is simply that customer's account printed out: opening balance, each invoice and payment, and the closing balance. An aging report, which sorts each customer's balance by how long it has been outstanding, is built from the same accounts, with each invoice carrying its date. Credit decisions, such as whether to accept another order from a customer who is behind, rely on the individual balance, not the control total. On the supplier side, deciding which bills to pay this week, and spotting a discount deadline, starts from each supplier's account.

The control account, by contrast, is what the general ledger and the financial statements need: one figure for receivables and one for payables. Keeping both, and proving they agree every month, gives the business detail where it needs detail and a clean total where it needs a total.

A month-end checklist

• Has every sale on account, payment and credit memo been posted to a customer or supplier?
• Have cash sales and cash purchases been left out of the subsidiary accounts?
• Does the schedule of balances total to the control account?
• If not, does the difference match a single transaction, or twice one (posted to the wrong side)?

Working through that list every month keeps both ledgers trustworthy, so that statements sent to customers and payments made to suppliers rest on balances everyone can rely on.

Common mistakes

1. Adding returns. A credit memo reduces what is owed, for customers and suppliers alike.
2. Posting cash sales or cash purchases to a customer or supplier account. Only transactions on account belong there.
3. Forgetting to update the control account. It changes by the same total as the subsidiary accounts.
4. Posting a payment to the wrong person. The totals still agree, so check names carefully.

How the practice works

Each exercise generates customers or suppliers with opening balances and a month of transactions. You enter each account's ending balance and the control account's ending balance, then press Check. Each amount is compared with balances computed from the same transactions, and recognised mistakes get specific feedback. The lesson starts with customer accounts, moves to supplier accounts, and finishes with longer months where cash transactions are mixed in and must be left out.