When should I use double instead of decimal?

Question

I can name three advantages to using double (or float) instead of decimal:

1. Uses less memory.
2. Faster because flo

Answer 1

Use decimal for base 10 values, e.g. financial calculations, as others have suggested.

But double is generally more accurate for arbitrary calculated values.

For example if you want to calculate the weight of each line in a portfolio, use double as the result will more nearly add up to 100%.

In the following example, doubleResult is closer to 1 than decimalResult:

// Add one third + one third + one third with decimal
decimal decimalValue = 1M / 3M;
decimal decimalResult = decimalValue + decimalValue + decimalValue;
// Add one third + one third + one third with double
double doubleValue = 1D / 3D;
double doubleResult = doubleValue + doubleValue + doubleValue;

So again taking the example of a portfolio:

• The market value of each line in the portfolio is a monetary value and would probably be best represented as decimal.

• The weight of each line in the portfolio (= Market Value / SUM(Market Value)) is usually better represented as double.