Bitcoin has a maximum supply of 21 million bitcoin in its consensus rules. That limit is not a marketing promise or a company policy. It is a rule that participants can verify while running compatible software.
A cap is different from the current supply
The total amount that can ever be issued and the amount already issued are different ideas. New bitcoin enters circulation through block subsidies paid to miners. Over time, those subsidies decline. The schedule is visible in the protocol and can be independently checked.
A fixed maximum does not tell us what any asset will cost, how it will be used, or what its future value will be. It only describes one part of Bitcoins monetary design.
Halvings slow new issuance
Approximately every four years, the block subsidy is cut in half. This event is called a halving. The exact timing depends on blocks, not a calendar appointment. Halvings continue until the subsidy becomes very small.
The halving schedule helps explain why issuance is front-loaded: more bitcoin was issued in earlier years than will be issued in later years. Transaction fees can still be included in blocks, but they are separate from the subsidy schedule.
Rules work because participants verify them
No single person needs to be trusted to maintain the cap. Nodes validate blocks against the rules they choose to run. A block that attempts to create more than the allowed subsidy can be rejected by nodes following those rules.
That does not mean Bitcoin never changes. Software can evolve when people voluntarily adopt compatible changes. The important distinction is that users can evaluate and choose the rules they accept rather than relying on a central issuer.
Understanding the supply cap is useful context, not a reason to rush into a purchase. This article is educational and not financial advice.