Profits Tax Return (BIR51) in Hong Kong: Filing Deadlines, Block Extensions and Penalties.

What the BIR51 is and when it arrives

The BIR51 is the profits tax return that Hong Kong's Inland Revenue Department (IRD) issues to corporations. Filing the BIR51 is how a company reports its assessable profits, or its loss, for a year of assessment, and its deadline sets the timetable for the audit and tax computation that go with it. Partnerships and other unincorporated businesses receive a BIR52 instead, and non-resident persons a BIR54.

Returns go out in a bulk issue on the first working day of April. On 1 April 2026 the IRD issued about 270,000 profits tax returns for the 2025/26 year of assessment, reminding taxpayers that they are generally required to file within one month, and that represented cases follow the dates in its Block Extension Letter.

A year of assessment runs from 1 April to 31 March, but a company is taxed on its own financial year. The return covers the accounts that end within that year of assessment, so a company with a 31 December 2025 year-end reports those accounts on its 2025/26 BIR51. The IRD calls this the basis period, and it is why the deadline that applies to a company depends on its accounting date.

Not every company receives a return every year. The IRD does not usually call for annual returns where a business has no assessable profits, has not started, or has stopped, but a return that has been issued must still be filed. A company that is chargeable to profits tax and has received no return has to write to the IRD for one within four months after the end of its basis period.

BIR51 deadlines and the Block Extension Scheme

The normal profits tax return deadline is short. A return should be filed within one month of its date of issue, and the exact compliance date is printed on page 1. For a company that files on its own, that printed date is the deadline, with one further month available on application if it files electronically.

Many companies work to later dates. When a company has appointed a tax representative, usually an accounting or tax firm, the representative can apply under the Block Extension Scheme, and the deadline then depends on the company's accounting date: the day its financial year ends. The IRD sorts accounting dates into three codes, N, D and M, and publishes the extended due dates for 2025/26 returns on GovHK.

Source: GovHK and Inland Revenue Department. Checked October 2026.

Three points sit behind the table:

• The D-code date moved. The IRD later issued a notice extending the due date for D-code returns, listed in its Tax Representatives' Corner. The D-code dates above are the ones GovHK showed when this guide was checked, and articles written in spring 2026 may show an earlier date.
• Applications are now electronic. From April 2026, tax representatives must submit block extension applications online through the Tax Representative Portal. The 2025/26 arrangements were set out in a circular letter dated 19 March 2026.
• Further extensions are exceptional. A further extension beyond the block extension date is granted only in the most exceptional circumstances, on a written request that explains the delay and comes with supporting evidence.

As of October 2026, the N and D dates for 2025/26 have passed, and the next date in the cycle is 16 November 2026 for profitable companies with January to March year-ends. Returns for 2026/27 will go out in the April 2027 bulk issue. The IRD publishes each year's block extension dates in a circular letter early in the year, so the 2026/27 dates are not out yet.

The first profits tax return for a new company

A new company does not receive a return in its first April. A newly registered business generally receives its first profits tax return some 18 months after it was incorporated or started business, and the first audit has to be finished in time to go with it. Our guide to company registration in Hong Kong puts that first return on one timeline with the other early filings.

The first return covers a special basis period for a business that has just started, so the first financial statements may cover more or less than 12 months. The IRD's FAQ on completing the BIR51 says figures from accounts covering a longer or shorter period are entered as they are, without apportioning or grossing them up.

Two points catch first-time filers out. Profits earned from the day business starts fall into that first basis period, even though the first return arrives many months later. And the assessable profits on the return set two figures: the profits tax for that year and the provisional profits tax for the following year. A tax representative can estimate what that first assessment is likely to ask for before the return goes in.

What goes with the BIR51

Every item on the return has to be completed, with "0" entered where there is nothing to report. A corporation with any gross income in the basis period must also file its supporting documents with the return, and the IRD sets them out on its page on completing profits tax returns.

Source: Inland Revenue Department. Checked October 2026.

Audited accounts. Audited financial statements go with the return in all cases except three: dormant companies under the Companies Ordinance, companies incorporated where the law does not require an audit and none was prepared, and Hong Kong branches of foreign companies that supply set information about the overseas audit and the branch's records. Only a CPA (practising), a CPA firm or a corporate practice registered with the Accounting and Financial Reporting Council can act as a company's auditor. Our guide on choosing a certified public accountant in Hong Kong explains how to check one, and you can compare audit firms in Hong Kong in the directory.

Small companies. Companies with gross income of HK$2 million or less used to be allowed to file the return on its own. The IRD now says they may no longer file without supporting documents such as financial statements and a tax computation, so older advice to the contrary is out of date.

Offshore claims. A company claiming that some or all of its profits arise outside Hong Kong must attach a statement of its reasons, and those reasons should be capable of being backed by evidence if the IRD asks for it.

Rates. Corporations pay 8.25% on the first HK$2 million of assessable profits and 16.5% on the rest; among connected entities only one can elect the lower tier, and the electing company lists its connected entities on Supplementary Form S1.

Records. The records behind the return should be kept for at least seven years after the transactions they relate to. Failing to keep sufficient business records can lead to a fine of up to HK$100,000.

Electronic filing and iXBRL

There are three ways to file a BIR51, and they differ mainly in the format of the attachments.

Source: Inland Revenue Department. Checked October 2026.

iXBRL (inline eXtensible Business Reporting Language) is a format that tags each figure in the accounts and the tax computation so that software can read it. The IRD publishes its own taxonomy and free iXBRL data preparation tools for converting accounts into that format.

Online filing runs through the Business Tax Portal for the company itself, or the Tax Representative Portal for its tax representative or service provider. Uploaded accounts and computations are validated, with the result provided within one working day, and a return filed online is signed electronically by a director, the secretary or a manager, or by a service provider holding the company's signed confirmation. The IRD's guide to electronic filing of profits tax returns walks through each step.

Who must e-file. Since 1 April 2026, the first phase of mandatory e-filing has applied to the Hong Kong entities of multinational groups within the global minimum tax rules, meaning groups with consolidated revenue of EUR 750 million or more in at least two of the four preceding fiscal years. These entities must e-file their profits tax returns for 2025/26 onwards, on a once-in, always-in basis. Semi-electronic filing is not accepted for them, and their extra month is automatic if they told the IRD their status before March 2026.

Everyone else. E-filing is voluntary, and a company that e-files can apply for a further month on top of its deadline. The IRD has said mandatory e-filing will move from large businesses to smaller entities in phases, but its iXBRL page gives no date for the next step. Supplementary forms are the exception that already applies to every company: they must be filed electronically, whatever mode the return itself uses.

Late filing: estimated assessments and penalties

If a return is not filed by the due date or the extended due date, the IRD issues an estimated assessment, and the company may be required to pay more tax. Penalty proceedings can follow, and in some cases prosecution.

For profits tax cases with no field audit or investigation, the IRD's penalty policy applies a loading scale for failing to file in time, measured as a percentage of the tax undercharged:

Source: Inland Revenue Department. Checked October 2026.

The percentages are guidance. The IRD adjusts them for the length of the delay, the amount of tax involved, the reasons given, and the attitude and remedial steps of the taxpayer. An earlier offence counts once a warning letter, compound offer, court fine or penalty assessment has been issued for it.

Behind the scale sit the statutory limits. Additional tax under section 82A of the Inland Revenue Ordinance can reach three times the tax undercharged, and prosecution for failing to file a return in time carries a fine of HK$10,000 plus a further fine of treble the tax undercharged. Before assessing additional tax, the IRD sends a written notice and allows at least 21 days for representations, and an additional tax assessment can be appealed to the Board of Review within one month.

Timing still matters once the deadline has passed: the scale loads a return filed after two or more estimated assessments more heavily than one filed after the first. The IRD's FAQ also allows an objection against an estimated assessment, made in the absence of a return, to be sent in the same envelope as the return itself.

Where a tax representative fits in

The IRD does not require a company to use a practising accountant to complete its return, and a director can sign it. Many companies still appoint a tax representative, and the timetable is a large part of the reason: the block extension dates in the table above apply only where a tax representative has applied for them.

The IRD treats two roles separately. A tax representative is appointed to handle the company's profits tax matters and can apply for block extensions on its behalf. Since 1 April 2022, a company can also engage a service provider just to furnish the return, after signing a confirmation (form IR1476) that the information is correct and complete. Either way, the company stays responsible for the return.

A tax representative typically prepares the tax computation, completes and files the BIR51, applies for the block extension, and deals with IRD questions after filing. Before engaging one, it helps to ask:

• Will you act as our tax representative, and which accounting-date code and due date apply to us this year?
• Will you e-file the return and apply for the extra month that e-filing allows?
• Who prepares the iXBRL files, and is that in the fee?
• Which supplementary forms do we need, including Form S1 if we have connected companies?
• Does the engagement cover IRD enquiries, objections and any estimated assessment?
• When do you need our audited accounts to meet the date?

To compare providers, see profits tax services in Hong Kong for return preparation, tax advisors in Hong Kong for broader IRD work, and accounting firms in Hong Kong for the books, audit coordination and filing calendar.

This guide is general information, not tax, accounting or legal advice. Filing dates and requirements change from year to year; for a specific company, speak with a qualified accountant or tax advisor.