ROUNDDOWN Function

The ROUNDDOWN function rounds numbers down. Unlike standard rounding, where only numbers less than 5 are rounded down, ROUNDDOWN rounds all numbers down. For example:

=ROUNDDOWN(3.999,0) // returns 3

ROUNDDOWN takes two arguments, number and num_digits. Number is the number to be rounded, and num_digits is the place at which number should be rounded. When num_digits is greater than zero, the ROUNDDOWN function rounds on the right side of the decimal point. When num_digits is less or equal to zero, the ROUNDDOWN function rounds on the left side of the decimal point. Use zero (0) for num_digits to round to the nearest integer. The table below summarizes this behavior:

How ROUNDDOWN works

The ROUNDDOWN function works like the ROUND function except that it always rounds down. The steps look like this:

1. Determine the precision. The precision is determined by the number of decimal places provided as the num_digits argument. For example, =ROUNDDOWN(A1,1) will round a number in A1 down to one decimal place, and =ROUNDDOWN(A1,0) will round down to the nearest whole number.

2. Determine the rounding digit. This is the number in the place you are rounding to. For example, when rounding to the nearest whole number, the last number to keep is in the 1s position.

3. Leave the rounding digit alone and treat the remaining digits to the right as zero. For example, to round the number 2.786 to the nearest tenth (i.e. 1 decimal place):

• The rounding digit is 7 (the first digit after the decimal).
• Treat the remaining digits as zero (2.700)
• The number becomes 2.7.

We can get the same result with the ROUNDDOWN function like this:

=ROUNDDOWN(2.786,0) // returns 2
=ROUNDDOWN(2.786,1) // returns 2.7
=ROUNDDOWN(2.786,2) // returns 2.78

The ROUNDDOWN function is closely related to the TRUNC function. In fact, I'm not aware of any situation where the two functions return different results. If you know of a case, please let me know.

Round to right of the decimal

To round down values to the right of the decimal point, use a positive number for num_digits: 

=ROUNDDOWN(A1,1) // Round down to nearest tenth (0.1)
=ROUNDDOWN(A1,2) // Round down to nearest hundredth (0.01)
=ROUNDDOWN(A1,3) // Round down to nearest thousandth (0.001)
=ROUNDDOWN(A1,4) // Round down to nearest ten-thousandth (0.0001)

The formulas above round a number in cell A1 down to the nearest 1 decimal place, the nearest 2 decimal places, the nearest 3 decimal places, and the nearest 4 decimal places.

Round to left of the decimal

To round down values to the left of the decimal point, use zero or a negative number for digits:  

=ROUNDDOWN(A1,0) // Round down to nearest 1
=ROUNDDOWN(A1,-1) // Round down to nearest 10
=ROUNDDOWN(A1,-2) // Round down to nearest 100
=ROUNDDOWN(A1,-3) // Round down to nearest 1000
=ROUNDDOWN(A1,-4) // Round down to nearest 10000

ROUNDDOWN with negative numbers

Excel's ROUNDDOWN function always rounds numbers down towards zero. You can see this behavior in the examples below, where the number to round is given as -2.786:

=ROUNDDOWN(-2.786,0) // returns -2
=ROUNDDOWN(-2.786,1) // returns -2.7
=ROUNDDOWN(-2.786,2) // returns -2.78

Although you might think negative numbers should become "more negative",  ROUNDDOWN consistently moves toward zero.

Nesting calculations inside ROUNDDOWN

Other operations and functions can be nested inside ROUNDDOWN. For example, to round down the result of A1 divided by B1, you can use a formula like this:

=ROUNDDOWN(A1/B1,0) // round down result to nearest integer

Other rounding functions

Excel provides several rounding functions, each with a different behavior:

• To round with standard rules, use the ROUND function.
• To round to the nearest multiple, use the MROUND function.
• To round down to the nearest specified place, use the ROUNDDOWN function.
• To round down to the nearest specified multiple, use the FLOOR function.
• To round up to the nearest specified place, use the ROUNDUP function.
• To round up to the nearest specified multiple, use the CEILING function.
• To round down and return an integer only, use the INT function.
• To truncate decimal places, use the TRUNC function.

Notes

• The ROUNDDOWN function rounds a number down to a given place by treating the remaining numbers as zero.
• If the number is already rounded down to the given number of places, no rounding occurs.
• If number is not numeric, ROUNDDOWN returns a #VALUE! error.
• If num_digits is not numeric, ROUNDDOWN returns a #VALUE! error.
• ROUNDDOWN always rounds numbers toward zero.