Why is .NET doing this?

[hqderivco]

In Visual Studio 2022 (17.14.9) in the Interactive window, when performing the following operation:

0.46 - 0.445

dotnet is returning 0.015000000000000013, why? I'm missing something?

[hqderivco]

Got an answer, closing the discussion:

This is due to how floating-point numbers are represented in binary format in computers. The number 0.46 - 0.445 should theoretically be exactly 0.015, but due to the way floating-point numbers work in binary, some decimal numbers cannot be represented exactly.
In binary floating-point arithmetic (which .NET uses with double type), numbers are stored in binary format, and not all decimal numbers can be represented exactly in binary. This leads to small rounding errors that you're seeing.
For example:
• 0.46 in binary floating-point is actually something like 0.45999999999999996
• 0.445 in binary floating-point is actually something like 0.44499999999999995
• When you subtract them, you get 0.015000000000000013
If you need exact decimal arithmetic, you should use the decimal type instead of double. The decimal type is designed for financial calculations and will give you exact decimal arithmetic (though it's slower than double).