The Bitcoin halving event, which cuts block rewards in half every four years, combined with a fixed maximum supply of 21 million BTC and sustained or increased demand, is expected to lead to significant price increases, potentially doubling or more due to speculation.
"every four years Bitcoin goes through a process called the h havinging basically this is when the amount of BTC that miners can earn as a block reward is cut in half The effect of this is that it restricts the amount of new BTC entering circulation and by the way BTC has a maximum supply of 21 million there will never be more than 21 million BTC in existence so the restriction of this already limited supply combined with the same or more demand for BTC eventually results in BTC's price doubling often more due to speculation"