Social Insurance at Two Jobs: Who Files, and What It Costs

The short answer: only people who meet the requirements at both places enrol twice

Sources: Japan Pension Service, "Procedures when you come to be employed by more than one establishment"[Japan Pension Service]; leaflet "To everyone working at two or more establishments through a second job or side work"[Japan Pension Service]

The enrolment requirements are judged separately for each employer; the hours at the two companies are not added together. Even if you work 40 hours a week at your main job, 15 hours a week at the side job means no enrolment there. Among the requirements for short-time workers, the wage requirement of "88,000 yen a month or more" was abolished in October 2026, so the pivot is now whether you work 20 hours a week or more. That change means more people will meet the requirements at a side job, so this topic will apply to more and more readers. For the requirements as a whole, see the 1.06 million and 1.3 million yen thresholds and the abolition of the wage requirement in October 2026.

The notification is filed "by you" "within 10 days" at a pension office

Ordinary social insurance procedures are handled by the company, but the two-or-more-establishments notification is a filing submitted by the insured person in person. The Japan Pension Service says to file it "within 10 days of the event" at the pension office with jurisdiction over the establishment you have selected (where you are covered by the Japan Health Insurance Association)[Japan Pension Service].

1. The side job files a notification of acquisition of insured status. Your side employer files your acquisition of insured status at the pension office as one of its own insured persons (a company procedure).
2. You file the "notification of selection of the affiliated establishment / employment at two or more establishments". You decide and enter which employer is the "principal establishment (selected establishment)". Normally you choose the main job with the higher pay. If you choose a company that belongs to a health insurance society, a filing with that society is needed as well.
3. The Japan Pension Service sets the combined standard monthly remuneration and notifies both companies. Each company is notified of its apportioned share of the premium, which is deducted from your pay from the following month.
4. Health insurance status is consolidated under the insurer of the selected establishment. Your My Number health insurance card keeps working, but your insured person's reference number with the Japan Health Insurance Association changes to a new one. Anyone who needs a certificate of eligibility is issued one by the Association.

Even if the filing is late, the enrolment date is backdated, so the premiums are deducted later in a lump. Once enrolment at the side job is settled, the safe course is to file within that same month.

How much do premiums rise? Combined, then apportioned by the ratio of pay

The Japan Pension Service's worked example has Company A, the selected establishment, paying 200,000 yen a month and Company B paying 100,000 yen a month. The standard monthly remuneration is set on the combined 300,000 yen, and the employee's half of the employees' pension premium (18.3%), 54,900 yen a month, comes to 27,450 yen, which is apportioned by the ratio of pay (200,000 to 100,000)[Japan Pension Service].

The important point here is that the 18,300 yen deducted at Company A is the same as the amount when you were enrolled at Company A alone (200,000 yen × 9.15% = 18,300 yen). Because the apportionment follows the ratio of pay, the premiums on your main job's payslip barely change. What changes is that premiums now apply to the side job's pay, at the same rate as the main job: employees' pension 9.15% plus health insurance about 5% (Japan Health Insurance Association, in a branch with a rate around 10%) = about 15%. From age 40, long-term care insurance adds about 0.8%.

Standard monthly remuneration runs in grades, so how the grade rounds up after combining produces differences of a few hundred yen. And for high earners whose combined remuneration exceeds the employees' pension ceiling (a standard monthly remuneration of 650,000 yen), the ceiling caps the total, so the premium on the side job's pay comes out lower than strict proportion.

When you enrol at a side job, that employer pays the same amount of premium as you do. That is the background to a side employer being reluctant to enrol you. Even so, failing to enrol someone who meets the requirements is against the law, and it is not something you get to choose.

Not only paying out: your pension and benefits grow on the combined base

In return for the higher premiums, your future old-age employees' pension is calculated on the combined remuneration. The earnings-related portion is "average standard remuneration × 5.481/1000 × months of coverage", so a side job of 100,000 yen a month kept up for a year adds about 6,600 yen a year to your pension, and ten years adds about 66,000 yen a year, for life. The employees' pension premiums paid on the side job come to about 1.1 million yen over ten years, so drawing the pension for about 17 years from age 65 (to age 82) breaks even.

Health insurance benefits are also set on the combined standard monthly remuneration. Injury and sickness allowance (two thirds of the standard monthly remuneration) when illness stops you working, and maternity allowance, are both based on an amount that includes the side job. Anyone who had been covering the side job through National Health Insurance and the National Pension (for instance someone whose main work is a sole proprietorship) gets stronger protection by switching to the employees' pension.

On the other hand, you cannot be covered by employment insurance in two places. Employment insurance covers you at the single company from which you draw your principal wage (apart from the special rule for people aged 65 or over who work 20 hours or more a week across two companies). If employment insurance premiums are being deducted at your side job, that is a mistake, so check it.

Will your main employer find out about the side job?

Yes. The Japan Pension Service sets the combined standard monthly remuneration and then notifies both companies of their respective apportioned premiums. Your main employer receives a determination notice showing apportioned premiums for a "person employed at two or more establishments", so anyone who looks at it can tell you are enrolled at another company. On the main job's side, too, your standard monthly remuneration no longer matches the grade that its own pay alone would produce.

If your employment rules ban side jobs or require permission, the practical course is to notify them before starting a side job on a scale that brings social insurance with it. On the tax side of a side job, the resident tax notice is another route by which side income can reach your main employer. For details, see filing a tax return for a side job.

When you are also the representative of your own company, and side jobs after 60

If an employee sets up their own corporation and draws director's remuneration from it, the representative of a corporation is covered by social insurance regardless of hours worked, so once director's remuneration arises the two-or-more-establishments notification is needed. The often-mentioned technique of "using a micro corporation to cut social insurance premiums" is aimed at people whose main work is a sole proprietorship; for a company employee who does both, the combination works in the direction of higher premiums. For how the mechanism works, see micro corporations and social insurance premiums. If you set director's remuneration at zero, you are not covered.

For people re-employed after 60 who work at two companies, the combined standard monthly remuneration is also used in the calculation of the in-work old-age pension (total remuneration equivalent). Since the threshold rose to 650,000 yen in April 2026, a pension plus pay from two companies above that amount means part of the pension is suspended.

Frequently asked questions

Summary

• If the side job also meets enrollment requirements, you must join social insurance at both workplaces, and you yourself must submit the Multiple Workplace Notification within 10 days.
• Enrollment requirements are judged separately for each workplace. At a company with under 20 hours a week or 50 or fewer employees, you generally do not need to enroll there for the side job.
• Premiums are determined by the standard monthly remuneration combining salary from both companies, prorated by the salary ratio. The main job's premium barely changes.
• While roughly 15% is newly deducted from the side-job salary, future employees' pension and sick leave allowance also increase based on the combined amount.
• Because both companies are notified of the prorated premium amounts, the main employer will also learn about the side job.

Reference links (sources)

This article is based on the materials below. Health insurance rates differ between the prefectural branches of the Japan Health Insurance Association and between health insurance societies, so the health insurance amounts in the table are indicative.

• Japan Pension Service, Procedures when you come to be employed by more than one establishment (the filing, the 10 days, combining and apportioning)
• Japan Pension Service, To everyone working at two or more establishments through a second job or side work (which working patterns are covered, the worked example of premiums)
• Japan Pension Service, Application of health insurance and employees' pension insurance to short-time workers (20 hours a week or more, the company-size requirement)
• MHLW, Employment insurance multi-job-holder scheme (the special rule combining two companies for people aged 65 or over)

Note: this article is general information. The premium amounts are estimates and change with grades and rates. For an individual decision, check with a pension office or your employer.