One Provider vs Big Four vs In-House Hire: Cost and Control for a Japan Subsidiary of 5 to 50 People

Choosing between one back-office provider, a Big Four firm, and an in-house hire is the decision about who runs the accounting, payroll, tax, and corporate filings of a Japan subsidiary, and on what cost and control terms. For a subsidiary of 5 to 50 people, the three models differ less in what gets done than in how costs behave as the entity grows, who holds the licences Japanese law requires, and how much of headquarters' time the arrangement consumes. This comparison is written for the group controller or regional finance lead who has to recommend one model to headquarters. It sets out how each model charges, where control sits, how the licence rules apply, and which model fits which kind of subsidiary.

Key Takeaways

• The three models solve different problems. A specialist provider runs day-to-day operations end to end, a Big Four engagement adds depth on complex tax and audit questions, and an in-house hire adds a person inside the business who knows its context.
• Cost behaviour matters more than headline fees. Provider fees scale with transactions and headcount, Big Four fees scale with hours and scope changes, and an in-house team is a fixed cost that also needs cover for leave and turnover.
• Licences apply to outsiders, not to the company itself. A provider or network firm that files for the subsidiary needs a zeirishi, a sharoushi, or a shiho-shoshi for the reserved work. An in-house team files as the company and needs expertise rather than a licence.
• Control depends on design, not on the model. Payment release, bank administrator rights, seal custody, and system access can be held by headquarters under any of the three models, and should be.
• Hybrids are an option. A subsidiary can pair a provider for operations with a group tax adviser for complex questions, then add an in-house finance lead once the entity is large enough to keep one person fully occupied.

The Three Back-Office Models for a Japan Subsidiary

A Japan subsidiary can buy its back office from a specialist provider, engage a Big Four network firm, or hire its own finance and HR staff.

Each model describes who does the work, not the scope, which is the same in all three: monthly bookkeeping and reporting, payroll and social insurance, the annual tax returns, and corporate registration changes. A specialist provider is a firm that runs these functions for foreign-owned companies as a managed service, usually coordinating the licensed professionals the work requires. A Big Four engagement places the work with a large international accounting network's Japan member firms, often as an extension of a global audit or tax relationship. An in-house hire means employing a finance or HR person in Japan, usually supported by outside professionals for the tax return and labour filings.

Demand for outsourced models continues to grow. According to Deloitte's Global Outsourcing Survey 2024, which polled more than 500 executives, 80% plan to maintain or increase investment in third-party outsourcing, and 70% say their vendor management function is not fully mature. The second figure is the one that matters for a small subsidiary: whichever model is chosen, headquarters still needs a way to direct and check the work.

How Each Model Charges a Japan Subsidiary

Provider fees track transactions and headcount, Big Four fees track hours and scope, and an in-house team is a fixed cost with hidden cover needs.

Comparing a monthly provider fee with an annual salary understates the in-house cost, and comparing either with a Big Four engagement letter understates the hourly work outside the defined scope. The table below compares how cost behaves in each model rather than what it amounts to, because the amounts depend on the subsidiary's headcount, transaction volume, and complexity. A twelve-month cost schedule on shared assumptions, as described in the guide to choosing a back-office provider for a Japan subsidiary, is the way to turn this into numbers.

Cost driver	Specialist provider	Big Four engagement	In-house hire
Basis of charge	Monthly fee by service, often tiered by volume	Annual engagement fee plus hourly rates	Salary, bonuses, and employer social insurance
Growth in headcount	Per-employee payroll fees rise	Scope and hours rise	Flat until a second hire is needed
Annual events (year-end adjustment, tax return)	Separate fees or included, by model	Usually separate engagements	Staff time, plus outside fees where expertise is lacking
Licensed professionals	Coordinated, billed separately or included	Usually within the network	Engaged separately where needed
Questions outside the scope	Hourly or a fair-use allowance	Hourly	Covered by salary, if the person has the expertise
Leave and turnover	Absorbed by the provider	Absorbed by the firm	Recruitment cost and a gap in cover
Software and systems	Often included or provided	Often the client's own systems	Licences bought by the subsidiary
Headquarters management time	Monthly review and approvals	Engagement management and approvals	Line management, review, and approvals

Control and Visibility for Headquarters

Headquarters keeps control of a Japan subsidiary in any model by holding payment release, bank administrator rights, seal custody, and system access.

A common assumption is that an in-house hire gives headquarters more control than an outside firm. In practice, control depends on how authority is designed, not on whose payroll the person sits. A single in-house accountant who records transactions, prepares payments, and holds the company seal concentrates more risk than a provider whose payment batches are released by an approver at headquarters. The same four controls apply in every model:

• Payment release by a named approver at headquarters, with bank administrator rights held by the company.
• Seal custody for the registered seal (実印, jitsuin) and bank seal, with a log of each use approved in advance.
• System access for headquarters to the accounting software and the e-filing accounts, with users removed when people change.
• A shared statutory calendar listing every filing, its owner, and its due date, reviewed at a fixed point each month.

Visibility is the second dimension. A provider or Big Four engagement produces a defined reporting package because it is contracted to; an in-house hire produces what headquarters asks for, which depends on how clearly the request is made. The common risks when payroll visibility is weak are covered in payroll compliance risks for foreign companies in Japan.

How Japan's Licence Rules Apply to Each Model

Japan's licence rules bind outside firms filing for a subsidiary, so providers and network firms need licensed staff while an in-house team does not.

Several parts of a subsidiary's back office are reserved by law for licensed professionals when done for others. The National Tax Agency's 2018 report on certified public tax accountants states that tax proxy, preparation of tax documents, and tax consultation must not be performed by anyone other than a zeirishi (税理士, certified public tax accountant), even at no charge; the report counted 77,327 registered zeirishi at the end of March 2018. Article 27 of the Social Insurance and Labour Consultant Act (社会保険労務士法) bars anyone other than a sharoushi from preparing or submitting labour and social insurance filings, or the related books and records, for others for a fee. The Japan Federation of Labor and Social Security Attorney's Associations puts the number of sharoushi at approximately 40,000. Article 73 of the Judicial Scrivener Act (司法書士法) reserves registration procedures, and the documents submitted to the Legal Affairs Bureau, for shiho-shoshi.

The rules apply differently to each model. A specialist provider either employs these professionals or coordinates partner firms, and the proposal should name them. A Big Four engagement normally draws on licensed professionals within the network, and the useful question is which network entity holds each licence and signs each filing. An in-house team files on behalf of its own employer, which is the company acting for itself, so the licence rules do not apply to it; the question there is whether the team has the expertise to prepare a corporate tax return or a labour insurance renewal correctly. JETRO's Experts Finder directory lists licensed professionals by category and is a useful cross-check on any firm named in a proposal.

Which Model Fits Which Japan Subsidiary

The right model for a Japan subsidiary depends on headcount, tax complexity, existing group relationships, and whether a local finance lead is needed.

No model is right for every subsidiary, and the right model can change as the entity grows. The scenarios below show where each model tends to fit; they are starting points for the selection, not rules.

Subsidiary profile	Model that usually fits	Why
Sales office of 5 people, simple transactions	Specialist provider	Full scope from one contact without a local finance hire
20 people with cross-border service fees and royalties to the parent	Specialist provider plus a group tax adviser	Operations stay with the provider; the tax questions go to the adviser
Group with a global audit and tax relationship already in place	Big Four engagement or a provider coordinated with it	Consistency with group audit and tax positions
Regional hub of 50 people with local management reporting needs	In-house finance lead plus a provider for payroll and filings	Enough work to keep one person occupied; the provider covers depth and leave
Subsidiary granting stock options to Japan employees	Provider with payroll and registration capability	Option registration and the related payroll filings recur each year
Dormant or wind-down entity	Specialist provider on a reduced scope	Annual filings and registrations continue with little activity

For the broader question of whether to outsource at all, including the hybrid model in detail, see outsourcing versus in-house back office in Japan. A comparison of named firms is in the Japan back office outsourcing providers guide.

Frequently Asked Questions

Is a Big Four firm necessary for a small Japan subsidiary?

Not usually. A Big Four engagement fits where the group already has a global audit or tax relationship, or where the subsidiary has complex tax positions. For day-to-day accounting, payroll, and filings in a subsidiary of 5 to 50 people, a specialist provider or a provider combined with a group tax adviser covers the same scope.

Can an in-house accountant file the subsidiary's tax return without a zeirishi?

Yes. The zeirishi rules restrict preparing tax returns for others, and an employee preparing the return of their own employer is the company filing for itself. The practical question is expertise: a corporate tax return and the related local tax filings require specialist knowledge that a single in-house accountant may not have.

When should a Japan subsidiary hire its own finance lead?

When there is enough recurring work to keep one person fully occupied, or when local management needs a finance partner in the business. Keeping a provider for payroll and statutory filings after the hire is one option, so the in-house lead covers analysis and decisions while the provider covers depth and leave.

Working with AQ Partners. Our Tokyo team provides back office operations for foreign companies operating in Japan, from monthly bookkeeping and annual tax filings to payroll coordination with a licensed sharoushi and corporate registration changes. Book a consultation to compare the models for your subsidiary.