Roughly every four years, the rate at which new Bitcoin is created gets cut in half. Miners (the computers running the network) used to earn 6.25 BTC per block; after the most recent halving in April 2024, they earn 3.125. The next halving is expected in 2028.
Why it matters: less new Bitcoin entering the market every day, but demand keeps growing. Basic supply and demand says price should drift higher. Historically, the 12-18 months after every halving have been Bitcoin's biggest bull markets.
It's not a guaranteed playbook. Past performance is not the future. But it's the closest thing crypto has to a clock, and it's why so many traders pay attention to where we are in the four-year cycle.