Client Accounting Services (CAS): A Guide for CPA Firms

Client Accounting Services — usually shortened to CAS — describes recurring accounting work a CPA firm performs for business clients. Rather than limiting the relationship to an annual tax return, the firm may maintain accounting records throughout the year and prepare periodic reports that help the client understand its financial position. The precise service is determined by the engagement, not by the CAS label alone.

A CAS engagement can connect several activities that are sometimes handled separately: bookkeeping, reconciliations, month-end close, financial statement preparation and management reporting. For the client, the value is a defined accounting process and a regular view of the records. For the firm, the work requires a clear service scope, a repeatable calendar and an agreed review process.

What a CAS engagement can include

The scope varies with the client's size, transaction activity, systems and reporting requirements. A basic recurring engagement may focus on transaction coding, bank and credit-card reconciliations and keeping the general ledger current. A broader engagement may include accounts payable and receivable records, payroll-related bookkeeping, balance-sheet schedules, month-end close and financial statement preparation.

Some firms also prepare management reports or additional schedules requested by the client. These deliverables should be named specifically. For example, “monthly reporting” could mean a profit and loss statement and balance sheet, or it could include department-level schedules, cash summaries and explanations of significant movements. A written list avoids different expectations about what the client will receive.

CAS does not automatically include every accounting, tax or advisory service. Tax return preparation, tax planning, budgeting, forecasting and CFO services should be treated as separate scopes unless the firm has explicitly included them and assigned the relevant responsibilities.

How CAS differs from annual tax compliance

Annual tax preparation is usually organized around the information needed to prepare and file a return for a particular tax year. CAS is organized around the accounting activity that takes place during the year. The two can complement each other: current books may make year-end tax preparation more organized, while tax requirements can inform the records and schedules the firm maintains.

They are still different engagements. A tax return has filing requirements and deadlines; a CAS engagement has recurring input dates, close procedures, reporting deliverables and review points. Firms should avoid treating bookkeeping completion as equivalent to tax-return readiness. Reconciliations, supporting records, adjustments and tax-specific information may still need to be addressed before a return can be prepared.

Recurring bookkeeping, close and reporting are connected

The monthly process generally begins with source information: bank activity, credit-card transactions, invoices, receipts, payroll records and other documents relevant to the agreed scope. Transactions are recorded using the firm's approved chart of accounts and coding rules. Reconciliations then compare ledger balances with bank statements, processor reports, loan statements or other source records.

Month-end close brings the period's work together. Depending on the engagement, it may include reviewing uncategorized transactions, preparing account schedules, identifying unusual balances, documenting proposed adjustments and assembling draft financial statements. The close checklist should distinguish completed work from items waiting on client information or professional judgment.

Reporting is the output of that process, not a substitute for it. A report is easier to review when the underlying balances tie to supporting schedules and open questions are visible. Firms should decide which reports are included, how often they are delivered, what comparisons or supporting schedules are expected and who approves the final package.

Define the boundary between production and advisory

A useful CAS operating model distinguishes preparation from interpretation. Production activities can include recording transactions, reconciling accounts, maintaining schedules and assembling reports. Professional review determines whether the records are complete and whether proposed treatments are appropriate. Advisory work interprets the information and discusses decisions with the client.

These responsibilities may sit with different people, but they should not be left implicit. The engagement and workflow should state who can approve adjustments, resolve accounting questions, explain results to the client and authorize the release of reports. If preparation is delegated to another person or provider, the CPA firm should define the workpaper format, evidence standard, review checklist and escalation path.

• Preparation: transaction processing, reconciliations, schedules and draft reporting packages within the agreed instructions.
• Professional review: evaluating exceptions, supporting evidence, proposed adjustments and whether the work meets the firm's standards.
• Client advice: interpreting results, making recommendations and discussing business or tax decisions with the client.

The precise allocation depends on the engagement and applicable professional requirements. A task list alone does not transfer the firm's responsibility for the professional decisions it has agreed to make.

Choose software around the firm's workflow

CAS practices use different accounting and reporting systems. QuickBooks Online and Xero are examples of bookkeeping platforms, while firms may also use bill-payment, expense-management, payroll, document collection and reporting applications. There is no single software stack that fits every CPA firm or client.

The important questions are operational: which system is the source of record, how transactions and supporting documents enter it, which integrations are enabled, who controls user permissions and what format the reviewer expects. If a firm works across several client systems, document the client-specific setup rather than assuming that one client's chart of accounts, close checklist or report template applies to another.

Where an external preparer is involved, confirm access rights and applicable confidentiality, contractual and taxpayer-information requirements before granting access. The firm should retain control of permissions and make sure the workflow supports its own review and record-retention procedures.

Build a practical CAS engagement scope

A clear scope makes recurring work easier to assign and review. It should identify the legal entities and accounts covered, the transaction and reconciliation tasks included, the close timetable, the reports to be prepared and the records the client must supply. It should also describe exclusions, approval responsibilities and how work changes are handled.

1. List the deliverables. Name the bookkeeping tasks, reconciliations, schedules and reports rather than relying on a broad phrase such as “full accounting.”
2. Set the calendar. Record client input dates, close milestones, review timing and the expected reporting date.
3. Define review criteria. Specify which accounts must reconcile, what support is required and how unresolved items are documented.
4. Assign decisions. Identify who approves adjustments, answers accounting questions and communicates conclusions to the client.
5. Record changes. Agree how new entities, additional reports, unusual transactions or changed deadlines affect the scope.

This structure also helps a firm assess whether the engagement is operating as intended. If a close repeatedly stalls because client records arrive late, the input process may need attention. If reviewers repeatedly request the same missing schedules, the workpaper standard may need clarification. If clients expect analysis that is not in the engagement, the firm should address the scope before the next reporting cycle.

When a firm considers outside production support

Some CPA firms evaluate whether defined preparation tasks can be completed by staff outside the core engagement team. That decision should start with the workflow, not with an assumption that every CAS task can be transferred. The firm needs to identify the work that is sufficiently documented, the systems and permissions involved, the evidence required and the person who will review the output.

A bounded pilot can help the firm evaluate a specific process. Select one client, period or task group; agree the input checklist and expected output; and record reviewer comments, missing information, corrections and unresolved questions. The result should be assessed against the firm's own acceptance criteria before the scope is changed or expanded.

For the commercial scope of recurring preparation work, see the CAS production support page for CPA firms. For the broader service model and other accounting workflows, see CPA firm support. The separate CPA-firm outsourcing readiness checklistcovers access, safeguards and operational preparation before a provider pilot.

Further reading for CPA firms

CAS is one part of a wider client accounting service model. Firms comparing operating approaches may also find it useful to review the guide to evaluating an accounting outsourcing partnerand the bookkeeping support overview. These pages address provider evaluation and recurring bookkeeping service scope separately from this guide's explanation of CAS.