Yes, you can absolutely buy half a bitcoin. In fact, you can buy much smaller fractions than that. Bitcoin was designed to be highly divisible, allowing anyone to participate regardless of whether they can afford a full "whole" coin. The Mechanics of Divisibility
Understanding Satoshis: Bitcoin's Smallest Unit and Its Value
A single bitcoin is not an indivisible unit like a physical gold bar; instead, it is more like a digital dollar that can be broken into cents.
Every bitcoin is divisible down to eight decimal places . The smallest possible unit is called a satoshi (or "sat"), named after Bitcoin’s pseudonymous creator, Satoshi Nakamoto.
Because the price of a full bitcoin has risen into the tens of thousands of dollars, most retail investors today do not purchase an entire coin at once.
One satoshi is equal to 0.00000001 BTC . There are 100 million satoshis in one full bitcoin.