Rounds a number down, toward zero.
Syntax
ROUNDDOWN(number,num_digits)
Number is any real number that you want rounded down.
Num_digits is the number of digits to which you want to round the number.
Remarks

ROUNDDOWN behaves like ROUND, except that it always rounds a number down.

If num_digits is greater than 0 (zero), then number is rounded down to the specified number of decimal places.

If num_digits is 0, then number is rounded down to the nearest integer.

If num_digits is less than 0, then number is rounded down to the left of the decimal point.
Examples
Formula 
Description (Result) 
=ROUNDDOWN(3.2, 0) 
Rounds 3.2 down to zero decimal places (3) 
=ROUNDDOWN(76.9,0) 
Rounds 76.9 down to zero decimal places (76) 
=ROUNDDOWN(3.14159, 3) 
Rounds 3.14159 down to three decimal places (3.141) 
=ROUNDDOWN(3.14159, 1) 
Rounds 3.14159 down to one decimal place (3.1) 
=ROUNDDOWN(31415.92654, 2) 
Rounds 31415.92654 down to 2 decimal places to the left of the decimal (31400) 