Client accounting services (aka CAS) is the fastest-growing accounting firm practice area. Learn how AP/AR automation helps you deliver it profitably, at scale, without adding headcount.
Client accounting services (CAS) is reshaping how accounting firms grow. Where tax and compliance work is cyclical and project-based, CAS is recurring, advisory, and built on ongoing relationships. For firms ready to scale it, the opportunity is significant. For firms trying to scale it manually, margin pressure arrives quickly.
The difference between a CAS practice that grows profitably and one that stalls at capacity usually comes down to one thing: whether AP and AR management is automated or handled by hand.
This guide covers what CAS is, why it is growing, and how payment automation enables accounting firms to deliver it at scale.
Client accounting services, or CAS, is a suite of outsourced accounting functions delivered by an accounting firm to business clients on an ongoing, subscription-style basis. Traditional CAS began with bookkeeping. Modern CAS now includes accounts payable, accounts receivable, payroll, financial reporting, and advisory.
The AICPA and CIMA formally recognize CAS as a distinct practice area, separate from compliance and tax work. The expanded term CAAS, standing for client accounting and advisory services, reflects the advisory layer that distinguishes leading CAS practices from basic outsourced bookkeeping.
See the AICPA's CAS practice standards and resources >
Bookkeeping records transactions after the fact. CAS manages the full accounting function: invoice approval, payment execution, reporting, and financial guidance.
The value proposition for clients is straightforward. They get a fully staffed accounting function without the full-time cost of one. For the firm, deeper relationships mean higher revenue per client and more predictable cash flow than compliance-only engagements.
CAS clients are SMB owners who do not want or cannot justify an in-house controller or CFO. Common profiles include scaling businesses with 10 to 100 employees and owners who want financial guidance rather than just monthly statements.
For accounting firms, the primary audience is their existing SMB client base, specifically clients who are underserved by compliance-only relationships.
CAS has consistently outpaced traditional compliance and tax services in revenue growth across the accounting profession. Accounting Today and the AICPA PCPS survey both track this annually. Firms offering CAS report higher client retention, deeper relationships, and higher average revenue per client than firms focused on compliance work alone.
The structural driver is clear: as cloud accounting software commoditizes basic bookkeeping, firms that add automation and advisory differentiate on value rather than on hours logged.
Recurring monthly revenue replaces project-based billing cycles, improving cash flow predictability for the firm. Deeper client relationships mean less churn and more natural expansion into additional services.
As Thomson Reuters Institute research on accounting firm transformation has shown, CAS margin depends on automation. Without it, firms bill at CAS rates while delivering at compliance-era labor costs. That math does not hold at scale.
CAS is labor-intensive when delivered manually. Every new client adds proportional work hours. Firms that scale without automation hit a ceiling fast: more clients, more staff, flattening margins.
Automation, particularly in AP and AR, is the lever that allows a firm to serve more clients per staff member without degrading service quality. AP automation for accountants and bookkeepers is what separates a CAS practice that scales profitably from one that stalls.
A well-structured CAS practice covers four functional areas:
Transaction management and bookkeeping. Daily or weekly categorization and coding of all transactions, bank feed reconciliation, and expense management. This is the foundation every other CAS service tier builds on.
Accounts payable management. Invoice capture, coding, and routing through approval workflows. Vendor payment execution via EFT, ACH, check, or international wire. AP aging monitoring and cash flow impact reporting. Accounts payable automation software handles the execution layer so staff can focus on exceptions rather than routine processing.
Accounts receivable management. Invoice creation and delivery to each client's customers. Payment collection, automated follow-up on overdue invoices, and collections reporting. Accounts receivable automation closes the collections loop without manual follow-up for every overdue balance.
Financial reporting and advisory. Monthly financial package including the P&L, balance sheet, and cash flow statement. KPI dashboards adapted to each client's business model. Quarterly advisory conversations on cash flow, working capital, and growth planning.
At 30 clients with 50 invoices each per month, the math on manual invoice processing stops working. Automation turns a multi-hour weekly task per client into a brief review of exceptions.
Automation captures invoices digitally, routes them for client approval, executes payments, and syncs everything to the accounting software without re-keying data. Two-way sync with QuickBooks and Xero is not optional in this model. Entries made in the payment platform must appear in the general ledger automatically. Otherwise, month-end close starts with catch-up work rather than verification.
Plooto's multi-entity model manages AP and AR across all client entities from a single firm login, each with configurable approval workflows, payment history, and a complete audit trail supporting client reporting. AR automation keeps invoices going out on schedule and reminders firing at set intervals, so collections status is always current without manual follow-up.
Building a scalable CAS practice requires standardized service tiers, a consistent technology stack, and repeatable workflows. Here is the build sequence:
|
Tier |
Services included |
Who it is for |
|
Entry |
Bookkeeping, monthly close, basic reporting |
SMBs new to outsourced accounting |
|
Standard |
Entry plus AP/AR management and payment execution |
Growing businesses with active payables and receivables |
|
Premium |
Standard plus advisory, cash flow forecasting, real-time dashboards |
Scaling businesses that need strategic financial guidance |
Transition bookkeeping records and clean up the chart of accounts. Connect the accounting software and payment automation platform. Set up approval workflows, identify client-side approvers, and establish the close timeline. Deliver a close calendar for the first quarter so the client knows exactly what to expect and when.
Week 1: Collect and process all vendor invoices for the prior period and route them for client approval. Weeks 2 to 3: Monitor payment status, follow up on AR aging, and handle ad hoc client requests. Week 4: Pre-close prep, confirming all AP and AR are current and flagging any missing entries. Days 1 to 5 of the new month: Close the period and generate the monthly financial package.
Automated weekly payment status summary so clients are not calling to ask what is paid. Monthly delivery of the full financial package with a brief written summary of notable items. Quarterly advisory call focused on trends, upcoming decisions, and financial planning.
The core requirements for a CAS technology stack:
Every tool in the stack must sync directly and automatically to the general ledger. Manual exports break the model. Two-way sync is required. Multi-entity capability is essential: the payment and AP/AR platform must support multiple client companies from a single firm login.
What to evaluate in a payment automation tool for CAS:
Hourly billing penalizes efficiency in CAS. Fixed-fee or subscription pricing captures the full value of the service regardless of the hours required to deliver it. As automation reduces delivery hours, margins improve without a rate increase.
Tiered packages give clients a clear entry point and a natural upgrade path as their business grows. The standard and premium tiers generate the strongest margins, and those margins only hold when AP and AR workflows are automated.
Communicating return on investment to prospective CAS clients is straightforward: they save on in-house accounting headcount, faster close enables faster financial decisions, AP automation prevents late payment fees, and AR automation shortens the time it takes to collect outstanding invoices.
As the Journal of Accountancy has noted in its CAS practice management research, firms that price on value rather than time consistently outperform their peers on both revenue per client and client retention.