How to Round Down in Python: Simple Guide with Examples

To round down in Python, use the math.floor() function which returns the largest integer less than or equal to a given number. Import math and call math.floor(your_number) to get the rounded down value.

Syntax

The math.floor() function rounds a number down to the nearest whole integer.

• math.floor(x): Returns the largest integer less than or equal to x.
• You must import math before using it.

python

import math

result = math.floor(3.7)
print(result)

Output

3

Example

This example shows how to round down different numbers using math.floor(). It works for positive and negative numbers.

python

import math

numbers = [3.7, 5.9, -2.3, -7.8]
rounded_down = [math.floor(num) for num in numbers]
print(rounded_down)

Output

[3, 5, -3, -8]

Common Pitfalls

One common mistake is using the built-in round() function expecting it to always round down. round() rounds to the nearest integer, not always down.

Also, forgetting to import math causes errors.

python

import math

# Wrong: round() does not always round down
print(round(3.7))  # Output: 4

# Right: use math.floor() to always round down
print(math.floor(3.7))  # Output: 3

Output

4
3

Quick Reference

Function	Description	Example	Output
math.floor(x)	Rounds down to nearest integer	math.floor(4.9)	4
round(x)	Rounds to nearest integer (not always down)	round(4.9)	5

Key Takeaways

Use math.floor() to round down numbers in Python.

Always import the math module before using math.floor().

round() does not always round down; it rounds to the nearest integer.

math.floor() works correctly with both positive and negative numbers.