Round Method (Decimal, Int32)

Math.Round Method (Decimal, Int32)

Updated: March 2012

Rounds a decimal value to a specified number of fractional digits.

Namespace:  System
Assembly:  mscorlib (in mscorlib.dll)

public static decimal Round(
	decimal d,
	int decimals
)

Parameters

d
Type: System.Decimal

A decimal number to be rounded.

decimals
Type: System.Int32

The number of decimal places in the return value.

Return Value

Type: System.Decimal
The number nearest to d that contains a number of fractional digits equal to decimals.

ExceptionCondition
ArgumentOutOfRangeException

decimals is less than 0 or greater than 28.

OverflowException

The result is outside the range of a Decimal.

The decimals parameter specifies the number of fractional digits in the return value and ranges from 0 to 28. If decimals is zero, an integer is returned.

This method is equivalent to calling the Round method with a mode argument of MidpointRounding.ToEven. If there is a single non-zero digit in d to the right of the decimals decimal position and its value is 5, the digit in the decimals position is rounded up if it is odd, or left unchanged if it is even. If d has fewer fractional digits than decimals, d is returned unchanged.

The behavior of this method follows IEEE Standard 754, section 4. This kind of rounding is sometimes called rounding to nearest, or banker's rounding. It minimizes rounding errors that result from consistently rounding a midpoint value in a single direction.

To control the type of rounding used by the Round(Decimal, Int32) method, call the Decimal.Round(Decimal, Int32, MidpointRounding) overload.

The following example demonstrates rounding to nearest.

Math.Round(3.44, 1); //Returns 3.4.
Math.Round(3.45, 1); //Returns 3.4.
Math.Round(3.46, 1); //Returns 3.5.

Math.Round(4.34, 1); // Returns 4.3
Math.Round(4.35, 1); // Returns 4.4
Math.Round(4.36, 1); // Returns 4.4

Windows 7, Windows Vista, Windows XP SP2, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP Starter Edition, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003, Windows Server 2000 SP4, Windows Millennium Edition, Windows 98, Windows CE, Windows Mobile for Smartphone, Windows Mobile for Pocket PC, Xbox 360, Zune

The .NET Framework and .NET Compact Framework do not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

.NET Framework

Supported in: 3.5, 3.0, 2.0, 1.1, 1.0

.NET Compact Framework

Supported in: 3.5, 2.0, 1.0

XNA Framework

Supported in: 3.0, 2.0, 1.0

Date

History

Reason

March 2012

Clarified midpoint rounding operation.

Customer feedback.

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