Client Onboarding Checklist for an Accounting Firm: The New-Client Pack

A client onboarding checklist for an accounting firm: the documents, notices and emails for a new client's first 30 days, with a worked UK bookkeeping example.

Written by Miriad with AI assistance and checked against the sources at the end. A working checklist for small accounting and bookkeeping firms, not legal advice: your engagement terms, your professional body and local law decide.

TL;DR: A new client's first 30 days set the tone for the whole relationship. The pack has three stages: engagement and due diligence (days 0 to 3), documents and access (days 4 to 14), and the first deliverable plus the deadline calendar (days 15 to 30). Include a written notice of the outside tools that will hold their data, and record how they found you.

A new bookkeeping client signs on a Thursday. By the following Wednesday they have received three separate emails asking for documents, none of which says what the documents are for, and nobody has told them which portal to use. They start to wonder whether they chose the right firm. Nothing went wrong technically. The firm simply had no pack.

This checklist turns client onboarding into a fixed set of documents and emails, so every new client gets the same first month. It belongs to our guide to accounting firm marketing strategies, because a good first month is where referrals start.

What belongs in a new-client pack for an accounting firm?

A new-client pack holds eight items: the engagement letter, the due diligence record, a written notice of the outside tools that will hold the client's data, any authorisation to act with the tax authority, a document request list or tax organizer, client portal access, a deadline calendar, and a 30-day check-in.

Item When Who prepares it Data level
Engagement letter Day 0 Partner Client file
Due diligence record (identity, ownership, source of funds) Day 0–3 Admin, partner signs Client file
Notice of outside tools that will hold their data Day 0–3 Admin, from a standard text Template only
Authorisation to act with the tax authority Day 0–3 Admin Client file
Document request list or tax organizer Day 4 Bookkeeper Template, then client file
Client portal access and a short how-to Day 4 Admin Client file
Deadline calendar for their year Day 15 Bookkeeper Template, then client file
30-day check-in call or email, plus "how did you find us?" Day 30 Partner Client file

The template column matters for AI. Every item starts from a standard text that holds no client data, and those standard texts can be drafted and improved with AI. The filled versions belong in the client file and in your practice management software.

Days 0 to 3: engagement, due diligence and notices

In the first three days, sign the engagement letter, complete any anti-money laundering client due diligence your country requires, tell the client in writing which outside tools will hold their data, and get any authorisation you need to act with the tax authority. These are the steps that are hard to fix later.

Due diligence. Check your own country's anti-money laundering rules for accountants. In Hungary, for example, anyone providing bookkeeping, tax adviser or tax consultancy services falls under the AML act and must carry out client due diligence when the business relationship is established (Pmt., Jogtár).

The tools notice. AICPA 1.150.040 says that before disclosing confidential client information to a third-party service provider, the member should inform the client, preferably in writing; this is not required for administrative support such as software application hosting or record storage (AICPA Code, 2024). A one-page notice listing the main tools (practice management software, client portal, any AI tool approved for client data) answers this before the client asks.

Authorisations. In the UK, an agent can sign a client up for Making Tax Digital for Income Tax, and for 2026–27 HMRC will not apply penalty points for late quarterly updates, though late returns and payments still attract penalties (GOV.UK, 2026). Put the sign-up on the day-3 list for every affected client.

Days 4 to 14: documents, portal and access

From day 4, send one document request list, not a stream of emails, and give the client portal access with a two-paragraph how-to. Group the requests by what they are for, so the client understands why each item matters. Agree on a single channel for documents, and never use plain email for bank statements or payroll files.

A document request list for a new bookkeeping client, grouped by purpose:

  1. To set up the books: last year's year-end accounts, the current chart of accounts or trial balance, opening balances.
  2. For bank reconciliation: access to bank feeds or the last three months of statements for each account.
  3. For accounts payable and accounts receivable: list of open supplier and customer invoices.
  4. For payroll (if included): employee list, pay details, last payroll reports.
  5. For tax: last filed returns, any letters from the tax authority this year.

Who sees the portal data matters too. The IRS security plan guidance asks firms to choose service providers whose contracts require them to maintain safeguards (IRS Publication 5708, 2024). Your client portal provider is one of them, and its contract should be in your security plan file.

Days 15 to 30: first deliverable, calendar and check-in

By day 30, deliver something the client can see: the first month-end close, a reconciled bank account, or a list of what is missing. Send their deadline calendar for the year, then hold a short check-in. At that check-in, ask and record how they found the firm.

The source question is worth keeping as a fixed field. Graham Archbold, founder of Chorus Insight, quoted in ACCA's Accountancy Business, suggests firms "verify the source of new business as part of their onboarding process" (ACCA AB, 2025). Asked at day 30, the answer is fresh, and a year of answers tells you where your clients come from.

The three emails of the pack, as short templates:

Welcome (day 0): Thank you for choosing us. Here is what happens in the next 30 days: (three stages, one line each). Your contact is (name). Attached: engagement letter and our notice on the tools that hold your data.

Document request (day 4): To set up your books we need the items below, grouped by what they are for. Please upload them to the portal (link) by (date). Please do not send bank statements by email.

Check-in (day 30): Your first month is done: (deliverable). Your deadline calendar is attached. Two questions: is anything unclear, and how did you first hear about us?

A filled-in example: a UK bookkeeper onboarding a sole trader

The example below runs the 30 days for a sole bookkeeper taking on a sole trader affected by Making Tax Digital. It uses the checklist above without changes, which is the point: the same pack works for every new client, and only the filled items differ.

Example (illustrative, not a real case): A sole bookkeeper takes on a self-employed electrician whose qualifying income is above the Making Tax Digital threshold.

Day Step Done by
0 Engagement letter signed through the portal; welcome email with the tools notice Bookkeeper
2 Identity and ownership checks recorded in the client file Bookkeeper
3 Client signed up for Making Tax Digital as agent Bookkeeper
4 Document request list sent: 5 groups, 14 items, due day 12 Bookkeeper
12 11 of 14 items received; one reminder for the 3 missing Bookkeeper
20 First month reconciled; quarterly update calendar sent Bookkeeper
30 15-minute check-in call; source recorded as "referral from a plumber client" Bookkeeper

The bookkeeper spends about 4 hours on this client's onboarding in total, most of it on the reconciliation. The templates took a day to write once and now take minutes to fill. Any marketing message that describes the service should not promise more than this process delivers: the ICAEW Code bans exaggerated claims, disparaging references and unsubstantiated comparisons in marketing (ICAEW Code, 2024).

How can AI help build the pack without client data?

AI can draft and improve every template in the pack, the welcome email, the document request list, the tools notice and the calendar layout, because none of them needs client data. The filled versions belong in your practice management software. Some small firms already use AI this way for onboarding and intake.

The Journal of Accountancy's August 2026 report on small firms describes an onboarding and tax organizer prototype and a prospect intake form routed into a work-management tool, with firms avoiding client data in public AI platforms and using enterprise versions (Journal of Accountancy, 2026). The same report names tools such as QuickBooks, Karbon, ClickUp, Microsoft Power Automate, Adobe Sign, ChatGPT, Copilot and Gemini.

The split that keeps it safe: write and improve templates in any tool, fill them only in the tools approved for client data. The rules for that split are in using AI without exposing client data, and the procedures manual article shows how this pack becomes one chapter of the firm's written procedures.

If you want the pack's standard texts, your services, fees, tools and rules, written down once so every AI draft starts from them, the Business Brain Starter Kit is built for that. Get notified when it launches.

FAQ

What should a client onboarding checklist for an accounting firm include?

Eight items: the engagement letter, the anti-money laundering due diligence record where required, a written notice of the outside tools that will hold the client's data, any authorisation to act with the tax authority, a grouped document request list or tax organizer, client portal access, a deadline calendar and a 30-day check-in that records how the client found you.

How long should onboarding a new accounting client take?

A useful target is 30 days from the signed engagement letter to the first visible deliverable and a check-in. Split it into three stages: engagement and due diligence in the first three days, documents and access by day 14, and the first deliverable plus the deadline calendar by day 30. The exact time depends on how complete the client's records are.

Do we need to tell new clients which software holds their data?

Under the AICPA Code, a member should inform the client, preferably in writing, before disclosing confidential client information to a third-party service provider, with an exception for administrative support such as software hosting or record storage. A one-page notice in the welcome email, listing the main tools, is a simple way to meet this.

Can AI write our client onboarding emails?

Yes, the standard templates can be drafted and improved with AI because they contain no client data. Fill in the client's details only inside your practice management software or another tool approved for client data. Have a qualified person check any template that explains deadlines or legal duties before it goes into use.

Sources

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