The bitcoin exchange rate corresponds to its value at a time T, or to its price on cryptocurrency platforms. Like all cryptocurrencies, the price of bitcoins is wholly determined according to supply and demand on these platforms.
The value of bitcoins is subject to very rapid upward and downward variations and is considered an extremely speculative asset. This is because it is a nascent technology offering a new system, the future of which is still uncertain. As a result, it is also considered to be a risky investment.