Using TinyTax as a Tax Agent for Multiple Companies

TinyTax is used by accountants and bookkeepers filing CT600 returns and Companies House accounts on behalf of client companies. This guide explains how the service works for agents and whether it suits your workflow.

Is TinyTax Suitable for Tax Agents?

Yes — TinyTax is designed to work for agents as well as company directors filing their own returns. You can manage all your client companies from a single dashboard and file each one using your own agent Government Gateway credentials.

If you are currently using HMRC's free CT600 filing service, note that it closed on 31 March 2026. Commercial software such as TinyTax is now the only way to file CT600 returns electronically.

How It Works for Agents

One Dashboard, Multiple Companies

Once you create an account, you add each client company to your dashboard by searching for it using the company name or number (drawn from Companies House). You can manage and file for as many companies as your plan covers from one login — no separate accounts needed.

Entering Your Figures

TinyTax is a year-end filing tool, not bookkeeping software. You bring the final figures from wherever you prepared them (a spreadsheet, accounting software, or your own workings) and enter them into TinyTax's online form.

The form covers:

Profit and loss — turnover, cost of sales, administrative expenses, interest, other income
Balance sheet — fixed assets, current assets, creditors, share capital, retained earnings

From those figures, TinyTax automatically generates:

The CT600 corporation tax return
A tax computation (showing how the liability was calculated)
Statutory accounts in iXBRL format (for both HMRC and Companies House)

If you prepare accounts in a spreadsheet, you enter the summary P&L and balance sheet figures into TinyTax's form — this typically takes 15–30 minutes per company once you are familiar with the layout.

Filing Using Your Agent Credentials

At the submission step, you will see a "Filing as" dropdown:

Select Tax agent and enter your own agent Government Gateway ID and password
Your clients do not need to provide their own Gateway credentials
HMRC must have an active agent authorisation on file for each company (via a 64-8 or online authorisation)

If you do not have formal agent authorisation for a particular client, you can switch to Company director mode and use the client's own Gateway credentials instead.

For Companies House, each company has its own 6-character authentication code — you (or your client) will need this when submitting accounts.

What Plan Do I Need?

If you are filing for more than one company, you need the Portfolio plan. This covers unlimited companies under a single annual subscription.

Visit tinytax.co.uk/pricing to see the current price.

You can sign up, add your companies, and enter all the figures before subscribing. You only need to pay when you are ready to submit. This lets you check the CT600 and accounts look correct before committing.

Common Questions

I prepare accounts in Excel — can I import them?

TinyTax does not accept a generic Excel file directly. You enter the summary profit and loss and balance sheet figures manually into the form. However, if any of your clients use accounting software (Xero, QuickBooks, Sage, FreeAgent), TinyTax has a trial balance import feature that can pre-populate many fields from a CSV export.

Do I need a separate account for each client?

No. You manage all clients from one login. Each client company is added to your dashboard as a separate entity.

My clients have different accounting year ends — is that a problem?

No. Each company has its own filing periods. You can work on and submit them independently at any time.

Can TinyTax file both the CT600 and Companies House accounts?

Yes — TinyTax files to both HMRC and Companies House. You submit the CT600 first, then submit accounts to Companies House (both from the same filing session).

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