What Happens When a Patent Expires?

Every patent has an expiration date. In the US, utility patents last 20 years from the filing date (with some adjustments for delays). After that, the invention enters the public domain, and anyone can use it freely.

The cliff effect

The pharmaceutical industry shows this most dramatically. When a blockbuster drug's patent expires, generic manufacturers flood the market within months. Prices can drop 80–90% within a year. The patent cliff is real and quantifiable — companies track it for years in advance.

The same happens in other industries, just less visibly. When core wireless communication patents expired, it opened space for new device manufacturers. When key semiconductor process patents aged out, the technology spread across the fab world.

What "public domain" actually means

Public domain doesn't just mean you can sell the product. It means:

• You can make, use, sell, and import the invention without a license
• You can describe exactly how it works in your product documentation
• You can build businesses entirely around the formerly patented technology
• You can even patent improvements to it (though not the original invention itself)

The only things that don't expire with the patent are trademarks and trade secrets. A company might lose patent protection on a drug's active compound but retain trademark protection on the brand name. That's why generic drugs have different names even when they're chemically identical.

The innovation that comes after

Patent expiration often spurs a second wave of innovation. With the core technology open, engineers can now focus on refinement, cost reduction, and combination with other technologies without licensing friction.

The internet itself is built substantially on expired patents. TCP/IP, Ethernet, core compression algorithms — these technologies spread precisely because their original protection lapsed and anyone could implement them.

Strategic expiration management

Large patent holders don't just sit on a single patent. They build portfolios — "patent thickets" — that layer multiple patents around a core invention, each expiring at different times. By the time the original patent expires, improvements are protected by newer patents, effectively extending control over the technology.

This is legal. It's also why some technologies never fully enter the public domain in a practical sense — the core patent expires but the most efficient implementations remain protected.

What to watch for

If you're tracking a technology space, patent expirations are predictable events that signal coming market changes. A 20-year-old patent filed during a major technology wave is expiring right now. That's an opportunity.