**Problem Formulation**: Given a float number. How to round the float down in Python?

Here are some examples of what you want to accomplish:

`42.52 --> 42`

`21.99999 --> 22`

`-0.1 --> -1`

`-2 --> -2`

**Solution**: If you have little time, here’s the most straightforward answer:

To round a positive or negative number `x`

down in Python, apply integer division `//`

to `x`

and divide by `1`

. Specifically, the expression `x//1`

will first perform normal float division and then throw away the remainder—effectively “rounding `x`

down”.

In general, there are multiple ways to round a float number `x`

down in Python: π

**Vanilla Python**: The expression`x//1`

will first perform normal division and then skip the remainder—effectively “rounding`x`

down”.**Round down**: The`math.floor(x)`

function rounds number`x`

down to the next full integer.**Round down (float representation)**: Alternatively,`numpy.floor(x)`

rounds down and returns a float representation of the next full integer (e.g.,`2.0`

instead of`2`

).**Round up**: The`math.ceil(x)`

function rounds number`x`

up to the next full integer.**Round up and down**: The Python built-in`round(x)`

function rounds`x`

up and down to the closest full integer.

Let’s dive into each of those and more options in the remaining article. I guarantee you’ll get out of it having learned at least a few new Python tricks in the process!

## Method 1: Integer Division (x//1)

The most straightforward way to round a positive or negative number `x`

down in Python is to use integer division `//`

by `1`

. The expression `x//1`

will first perform normal division and then skip the remainder—effectively “rounding `x`

down”.

For example:

`42.52//1 == 42`

`21.99//1 == 21`

`-0.1//1 == -1`

`-2//1 == -2`

This trick works for positive and negative numbers—beautiful isn’t it? π»

Here are a couple of Python code examples:

def round_down(x): return x//1 print(round_down(42.52)) # 42 print(round_down(21.99999)) # 21 print(round_down(-0.1)) # -1 print(round_down(-2)) # -2

π **Info**: The double-backslash `//`

operator performs integer division and the single-backslash `/`

operator performs float division. An example for integer division is `40//11 = 3`

. An example for float division is `40/11 = 3.6363636363636362`

.

Feel free to watch the following video for some repetition or learning:

## Method 2: math.floor()

To round a number down in Python, import the `math`

library with `import math`

, and call `math.floor(number)`

.

The function returns the floor of the specified `number`

that is defined as the largest integer less than or equal to `number`

.

π‘ **Note**: The `math.floor()`

function correctly rounds down floats to the next-smaller full integer for ** positive and negative integers**.

Here’s a code example that rounds our five numbers down to the next-smaller full integer:

import math print(math.floor(42.52)) # 42 print(math.floor(21.99999)) # 21 print(math.floor(-0.1)) # -1 print(math.floor(-2)) # -2

The following video shows the `math.floor()`

as well as the `math.ceil()`

functions — feel free to watch it to gain a deeper understanding:

## Method 3: np.floor()

To round a number down in Python, import the NumPy library with `import numpy as np`

, and call `np.floor(number)`

.

β
**Recommended**: How to Install NumPy?

The function returns the floor of the specified `number`

that is defined as the largest integer less than or equal to `number`

.

Here’s an example:

import numpy as np print(np.floor(42.52)) # 42.0 print(np.floor(21.99999)) # 21.0 print(np.floor(-0.1)) # -1.0 print(np.floor(-2)) # -2.0

Both `math.floor()`

and `np.floor()`

round down to the next full integer. The difference between `math.floor()`

and `np.floor()`

is that the former returns an integer and the latter returns a float value.

## Method 4: int(x)

Use the `int(x)`

function to round a positive number `x>0`

down to the next integer. For example, `int(42.99)`

rounds `42.99`

down to the answer `42`

.

Here’s an example for positive numbers where `int()`

will round down:

print(int(42.52)) # 42 print(int(21.99999)) # 21

However, if the number is negative, the function `int()`

will round up! Here’s an example for negative numbers:

print(int(-0.1)) # 0 print(int(-2)) # -2

Before I show you how to overcome this limitation for negative numbers, feel free to watch my explainer video on this function here:

## Method 5: int(x) – bool(x%1)

You can also use the following vanilla Python snippet to round a number `x`

down to the next full integer:

- If
`x`

is positive, round down by calling`int(x)`

. - If
`x`

is negative, round up by calling`int(x) - bool(x%1)`

.

**Explanation**: Any non-zero expression passed into the `bool()`

function will yield `True`

which is represented by integer 1.

The modulo expression `x%1`

returns the decimal part of `x`

.

- If it is non-zero, we subtract
`bool(x%1) == 1`

, i.e., we round down. - If it is zero (for whole numbers), we subtract
`bool(x%1) == 0`

, i.e., we’re already done.

Here’s what this looks like in a simple Python function:

def round_down(x): if x<0: return int(x) - bool(x%1) return int(x) print(round_down(42.52)) # 42 print(round_down(21.99999)) # 21 print(round_down(-0.1)) # -1 print(round_down(-2)) # -2

Alternatively, you can use the following slight variation of the function definition:

def round_down(x): if x<0: return int(x) - int(x)!=x return int(x)

## Method 6: round()

π‘ *This method is probably not exactly what you want because it rounds a number up and down, depending on whether the number is closer to the smaller or larger next full integer. However, I’ll still mention it for comprehensibility.*

Pythonβs built-in `round()`

function takes two input arguments:

- a
`number`

and - an optional
`precision`

in decimal digits.

**It rounds the number to the given precision and returns the result.** The return value has the same type as the input numberβor integer if the `precision`

argument is omitted.

Per default, the precision is set to 0 digits, so `round(3.14)`

results in `3`

.

Here are three examples using the `round()`

function—that show that it doesn’t exactly solve our problem.

import math print(round(42.42)) # 42 print(round(21.00001)) # 21 print(round(-0.1)) # 0

Again, we have a video on the `round()`

function — feel free to watch for maximum learning!

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