Kotlin How to Convert Double to Int with Examples

In Kotlin, you can convert a Double to an Int by calling the toInt() function on the double value, like val intValue = doubleValue.toInt().

Examples

Input12.99

Output12

Input0.0

Output0

Input-5.75

Output-5

How to Think About It

To convert a double to an int in Kotlin, think about removing the decimal part since an int holds whole numbers only. The toInt() function cuts off the decimal part without rounding, so you get just the integer portion of the double.

Algorithm

1

Take the double value as input.

2

Call the <code>toInt()</code> function on the double value.

3

Store or return the resulting integer value.

Code

kotlin

fun main() {
    val doubleValue: Double = 12.99
    val intValue: Int = doubleValue.toInt()
    println(intValue)  // Output: 12
}

Output

12

Dry Run

Let's trace converting 12.99 to int using toInt()

1

Start with double value

doubleValue = 12.99

2

Convert to int

intValue = doubleValue.toInt() -> 12

3

Print result

Output: 12

doubleValue	intValue
12.99	12

Why This Works

Step 1: Using toInt() function

The toInt() function converts a double to an int by dropping the decimal part.

Step 2: No rounding happens

It simply truncates the decimal, so 12.99 becomes 12, not 13.

Step 3: Result is an integer

The result is a whole number stored as an Int type.

Alternative Approaches

Using Math.round() and converting to Int

kotlin

fun main() {
    val doubleValue = 12.99
    val intValue = Math.round(doubleValue).toInt()
    println(intValue)  // Output: 13
}

This rounds the double to the nearest integer before converting, unlike toInt() which truncates.

Using floor() from kotlin.math and converting to Int

kotlin

import kotlin.math.floor
fun main() {
    val doubleValue = 12.99
    val intValue = floor(doubleValue).toInt()
    println(intValue)  // Output: 12
}

This explicitly floors the value before converting, similar to toInt() but clearer for some.

Complexity: O(1) time, O(1) space

Time Complexity

Conversion using toInt() is a simple operation that runs in constant time.

Space Complexity

No extra memory is needed besides the output integer, so space is constant.

Which Approach is Fastest?

toInt() is fastest and simplest; rounding or flooring adds minor overhead but is still O(1).

Approach	Time	Space	Best For
toInt()	O(1)	O(1)	Simple truncation without rounding
Math.round() then toInt()	O(1)	O(1)	Rounding to nearest integer
floor() then toInt()	O(1)	O(1)	Explicit floor before conversion