"How long does a patent last?" sounds like it should have one answer. It doesn't — the term depends on the type of patent, when you filed, and whether you keep it in force. Here's the clear version.
The three timelines
A temporary placeholder. It can't be renewed or extended; you convert to a utility application within the year or it lapses.
Measured from your earliest non-provisional filing date, as long as you pay the required maintenance fees along the way.
Protects how a product looks (not how it works), measured from the grant date, with no maintenance fees.
Why "up to" 20 years
A utility patent's clock starts at the filing date, not the grant date — and examination can take a few years. So if it takes three years to grant, you effectively have around 17 years of enforceable protection left. This is one reason your filing date matters so much: the sooner you file, the sooner that clock starts and the sooner your priority is locked.
A granted utility patent isn't "set and forget." You must pay maintenance fees at set intervals to keep it in force for the full term. Miss them, and the patent expires early — which is exactly how many patents become abandoned and open for others to build on.
What happens when it ends
When a patent expires — whether at the end of its term or because fees went unpaid — the invention enters the public domain. Anyone can then make, use, or sell it freely. That's the flip side of protection, and the reason abandoned patents can become a rich source of new opportunities.
This is general information, not legal advice. Specific cases can differ.
Start the clock the right way
Since a patent's term runs from your filing date, filing sooner is almost always better. AutoInvent turns your idea into patent-style text and sketches and guides you step-by-step through filing your provisional yourself with the USPTO — idea to filed provisional in under 10 minutes, for a couple hundred dollars plus the USPTO fee. Lock in your date now and keep the full runway ahead of you.