If you're seeking patent protection in Japan based on an earlier filing, you'll generally choose between two routes: filing directly in Japan under the Paris Convention, or entering the Japanese national phase through the PCT. The essential difference is timing. The Paris route requires you to file in Japan within 12 months of your first filing. The PCT route lets you defer that decision until 30 months.

Why this matters

Your choice of route affects more than timing—it shapes your cost planning, prosecution strategy, and how much information you'll have in hand before you enter Japan.

Paris direct filing tends to suit situations where Japan is clearly an important market from the outset and you want prosecution moving there sooner. It's also often simpler and more cost-effective when you're only filing in a handful of countries.

The PCT route works well when you need more time to assess whether the Japanese market justifies the investment. The international search report can help you evaluate the prior art landscape and sharpen your claim strategy before committing to Japan.

Practical points

With the Paris route, the main upside is early entry into Japan. The trade-off is that you must make the filing decision by the 12-month priority deadline, and translation and local filing costs come due at that early stage. Because the scope of later amendments and divisional applications is shaped by the translated text, the quality of the Japanese translation matters from the outset—and the Paris route gives you less time to get it right.

With the PCT route, the main upside is flexibility. You can wait up to 30 months before entering Japan, review the international search results, and decide whether to pursue Article 19 or Article 34 amendments, or leverage PCT-PPH. The trade-off is the added PCT-stage fees and procedures, and the fact that Japanese prosecution will start later if you defer national phase entry.

What to prepare for Japanese counsel

When you're ready to file in Japan, your Japanese counsel will typically need the following:

For Paris direct filing

• Priority information, plus the priority document or DAS access code
• Application documents for the Japanese filing
• Applicant and inventor details
• A Japanese translation—or instructions to use the foreign-language filing route (more on this in a later instalment)

For PCT national phase entry

• PCT application number and publication details
• PCT application documents for national phase entry
• Any Article 19 or Article 34 amendments
• A Japanese translation of the national phase text

Takeaway

Paris direct filing gets your case into Japan sooner. The PCT route buys you time to decide and refine your approach. The practical question isn't just when to enter Japan—it's what text and claim strategy you want to bring with you when you do.