What about workers' compensation when you are injured during a side job? Benefits for multiple-employment workers and the aggregation of wages

In short: For someone employed by two or more companies who is injured or falls ill while working, an amendment in force since September 1, 2020 (Reiwa 2) means the daily benefit base amount — the basis for workers' compensation — is calculated by aggregating the wages of all workplaces (Industrial Accident Compensation Insurance Act, Article 8, paragraph 3). Also, a framework called a "multiple-work-factor disaster," which evaluates the work of several companies together, was created (Article 7, paragraph 1, item 2), so overload that no single company alone would recognize as work-related can be assessed across companies. This article sets out who the "multiple-employment worker" is, the aggregation of wages, the multiple-work-factor disaster, the window for claims, and what the company should have in place.

"One of our employees was injured at their side job," "We allow side jobs, but what happens with workers' compensation?" — such consultations are increasing. This page is for the labour staff of small and medium-sized companies that employ side-job workers, or whose own employees have side jobs, and sets out how workers' compensation benefits for multiple-employment workers are approached. Whether a particular benefit is payable is decided by the Labour Standards Inspection Office and is outside the scope of this article.

What is a multiple-employment worker, and who is covered?

A "multiple-employment worker" is a worker who, at the time the injury or illness arises, is simultaneously employed by two or more businesses with different employers. A typical example is someone who is a full-time employee of Company A on weekdays and works part-time at Company B on weekends.

There is a line to watch.

Covered	Not covered (in principle)
A person simultaneously "employed" by two or more companies	A person whose side job is not employment (a side job as a sole proprietor / freelancer)
A person simultaneously used by two or more businesses with different employers	A person who has already left a previous job and works for only one company
A person working in more than one capacity, including special enrollment (in certain cases)	—

The key is being "used as a worker, simultaneously, by two or more businesses." Merely taking on other work as a freelancer does not, in principle, make one a multiple-employment worker (the approach to worker status is set out in our separate article, The line between subcontracting and employment).

Are injuries at the side job calculated using both companies' wages?

Yes. This is the heart of the September 2020 amendment. Workers' compensation benefits such as the absence (compensation) benefit are calculated on the basis of the "daily benefit base amount," but before the amendment, only the wages of the workplace where the disaster occurred were used. The wages at the side job dropped out, and the benefit was lower than the actual income.

After the amendment, for a multiple-employment worker, the amount obtained by aggregating the wages of all workplaces is the basis for calculating the daily benefit base amount (Industrial Accident Compensation Insurance Act, Article 8, paragraph 3).

	Before amendment (until August 2020)	After amendment (from September 1, 2020)
Calculating the daily benefit base amount	Only the wages of the one company where the disaster occurred	Aggregate of the wages of all workplaces
Example: a person earning 200,000 yen at A + 100,000 yen at B is injured at B	Calculated using only B's 100,000 yen	Calculated using the aggregated 300,000 yen as the basis

As a result, the absence benefit, disability benefit, survivor benefit, and so on come closer to the actual income level.

What is a multiple-work-factor disaster (brain / heart disease, etc.)?

Another pillar is the "multiple-work-factor disaster." This is an injury or illness caused by the work of two or more businesses of a multiple-employment worker (Industrial Accident Compensation Insurance Act, Article 7, paragraph 1, item 2). What it covers is mainly types such as brain and heart disease, and mental disorders, that arise from accumulated long hours and stress.

Previously, whether something was work-related was judged on the work overload of a single workplace alone. So if neither Company A nor Company B reached the recognition standard on its own, it could fail to be recognized as work-related at either. After the amendment, the system evaluates the working hours and stress of Company A and Company B together on an overall basis, and it can be recognized as a multiple-work-factor disaster.

Workers' compensation is organized into the following three types.

Type	Content
Work disaster	Injury or illness caused by the work of a single workplace
Multiple-work-factor disaster	Injury or illness (brain / heart disease, mental disorders, etc.) evaluated by combining the work of two or more businesses of a multiple-employment worker
Commuting disaster	Injury or illness caused by commuting

Note that even where it is not recognized as a multiple-work-factor disaster, it may still be recognized as a work disaster on the work of one company alone. It is judged in this order: first evaluate it as a work disaster, and where it is not recognized that way, evaluate it as a multiple-work-factor disaster.

Through which company is the workers' compensation claim made?

Workers' compensation benefits are received by the injured worker (or, in the case of death, the surviving family) making a claim to the Labour Standards Inspection Office. For a multiple-employment worker, the claim form must list all workplaces, and the wage amounts and so on must be certified by each workplace.

Have a question about your situation?

Tell us about your social insurance, payroll or employment enquiry.

Chat on LINEContact us

• The place of submission is the Labour Standards Inspection Office with jurisdiction over the workplace where the disaster occurred (for a multiple-work-factor disaster, the office with jurisdiction over the main workplace)
• The claim form has a field to state "whether there are other places of employment," and the wage amount of the non-disaster workplace is also declared
• The employer of each workplace certifies the working hours, wages, circumstances of the disaster, and so on

The company's role centers on certifying the required matters correctly. Whether the benefit is payable is decided by the Labour Standards Inspection Office; it is not something the company or a Shakai Hoken Roumushi decides. The flow of the claim procedure itself is also set out in our separate article, The workers' compensation procedure.

What should the company check and put in place?

If you allow side jobs, or if your own employees have side jobs, having the following in place for workers' compensation means you will not be caught off guard when the time comes.

What to do	Content
Grasp side jobs	Grasp, through notification and the like, whether an employee is also employed and working at another company
Put the work rules in order	Set the treatment of side jobs and the notification rules in the work rules
Keep records of wages and hours	Keep accurate records of your own wages and working hours, ready for certification
Confirm the point of contact	Share within the company the flow of the claim and whom to consult when a workers' compensation event occurs

The aggregation of working hours where there is a side job (managing overtime) is a separate issue from workers' compensation, but it is safer to organize it together. For details, see our separate article, Labour management of side jobs.

What can 四葉社会保険労務士事務所 do for you?

四葉社会保険労務士事務所 in Kohinata, Bunkyo Ward, handles support for workers' compensation claims (including benefits for multiple-employment workers), putting work rules that accommodate side jobs in order, and building a system for recording working hours and wages. The initial consultation is free. Fees are set out in the fee schedule.

Whether a benefit is payable is decided by the Labour Standards Inspection Office. This office is in the position of helping so that the claim can be made properly, and does not guarantee the outcome of the recognition.

Frequently asked questions

Q. If the side job is not part-time employment but a sole proprietorship, is it still aggregated?
A. In principle it is not subject to aggregation. The aggregation of the daily benefit base amount and the multiple-work-factor disaster apply to a multiple-employment worker who is "used as a worker in two or more businesses." A side job as a sole proprietor or freelancer, not being employment as a worker, is in principle not covered (exceptional treatment, such as where special enrollment applies, needs to be checked individually).

Q. From when does the aggregation of the daily benefit base amount apply?
A. It applies to injuries and illnesses that arise on or after September 1, 2020 (Reiwa 2). Disasters before that are calculated, as before, using only the wages of the workplace where the disaster occurred.

Q. Neither Company A nor Company B reaches the workers' compensation standard on its own. Can no benefit be received?
A. There is a possibility of being evaluated as a multiple-work-factor disaster, combining the work of both companies. For brain / heart disease, mental disorders, and the like, even where the overload of one company alone does not reach the standard, it is evaluated in aggregate if the person is a multiple-employment worker. The final recognition is made by the Labour Standards Inspection Office.

Q. Which company handles the claim procedure?
A. A workers' compensation claim is made by the worker (or surviving family), and the company does not have an obligation to make the claim on their behalf. However, the company is in the position of certifying the wages, working hours, circumstances of the disaster, and so on. For a multiple-employment worker, certification from all workplaces becomes necessary.

Sources for this article

• Industrial Accident Compensation Insurance Act (労働者災害補償保険法, Act No. 50 of 1947), Article 7, paragraph 1, item 2 (multiple-work-factor disaster), Article 8, paragraph 3 (the daily benefit base amount of a multiple-employment worker = aggregate of the amounts calculated for each business), and Article 20-2 onward (insurance benefits relating to multiple-employment workers)
• The multiple-employment-worker and multiple-work-factor-disaster systems came into force on September 1, 2020 (Reiwa 2) under the Act partially amending the Employment Insurance Act and others
• The definition of a multiple-employment worker (that, at the time the injury or illness arises, the person is simultaneously used by two or more businesses with different employers, and that a side job as a sole proprietor is in principle not covered), what a multiple-work-factor disaster covers (brain / heart disease, mental disorders, etc.), the aggregation of wages, the "whether there are other places of employment" field on the claim form, and the approach to where to submit the claim, are confirmed from the Ministry of Health, Labour and Welfare's "Workers' Compensation Benefits for Multiple-Employment Workers — An Easy-to-Understand Explanation (in force September 2020)" and materials published by prefectural labour bureaus (referenced September 2026)
• The article numbers and the date of entry into force have been checked against e-Gov Law Search and materials published by the Ministry of Health, Labour and Welfare

This article is general information. Judgments that fit your particular circumstances are made by a qualified professional after a meeting. Written by Joji Uramatsu (Shakai Hoken Roumushi (Certified Social Insurance and Labor Consultant), Gyoseishoshi (Certified Administrative Procedures Legal Specialist), Registered Real Estate Transaction Specialist).