How to use the TRUNC function

What is the TRUNC function?

The TRUNC function removes the fractional part of the number to an integer. Trunc stands for truncate meaning in this context removing the decimal part leaving only the integer.

1. Introduction

What is the fractional part of a number?

The fractional part of a number is the portion after the decimal point. It represents the fractional remainder when dividing a number into integer parts.

For a number x, the fractional part is denoted as: {x} The fractional part is equal to x minus the integer part of x.

For example,  x = 5.921 The integer part of x is 5 (rounded down)

The fractional part is: {x} = x - integer part of x
5.921- 5 equals 0.921

What is a fractional remainder?

The fractional remainder or fractional part refers to the non-integer portion left over after dividing a number by an integer.

For example, if we divide 5 by 2: 5 / 2 = 2 with fractional remainder 1 2*2 + 1 = 5

The integer quotient is 2, but there is a remaining fractional amount of 1 left.

What is an integer?

An integer is a whole number that can be positive, negative, or zero.

What is the difference between the TRUNC function and the ROUND function?

The ROUND function rounds a number to a specified number of digits while the TRUNC function removes digits based on the precision of the truncation that you specify.

For example, TRUNC(11.9345,0) returns 11 and ROUND(11.9345,0) returns 12

How to round numbers?

Rounding is a method to simplify a number by reducing its digits while keeping its approximate value close to the original value.

There are a few common ways to round:

• Round to a set number of decimal places, rounding 2.13579 to 2 decimal places gives 2.14.
• Round up or down to the nearest integer, rounding up 2.3 gives 3. Rounding down 2.3 gives 2.
• Round to a set increment, rounding to the nearest 10 rounds 17 to 20.
• Round to significant figures, rounding 2.333 to 3 significant figures gives 2.33.

When rounding, look at the first digit after where you want to round. If it's 5 or more, round up. If less than 5, round down. Rounding makes numbers cleaner and easier to work with in many everyday situations, however, they may also cause rounding errors like rounded values can compound errors. Rounding measurements and constants may reduces precision. It is better to round numbers after performing calculations than before.

What is the difference between TRUNC function and the TRIM function?

TRUNC truncates numbers to a specified number of decimal places. For example:

TRUNC(193.459, 2) = 193.45

TRIM removes leading, trailing, and excess whitespace from text. For example:

TRIM(" Orange ") = "Orange"

What is the difference between the TRUNC function and the INT function?

The INT function extracts the integer part of a number while the TRUNC function lets you specify the precision of the truncation.

For example, TRUNC(11.2345,1) returns 11.2 and INT(11.2345) returns 11

2. Syntax

TRUNC(number, [num_digits])

number	Required. The number you want to truncate.
[num_digits]	Optional. A number specifying the precision of the truncation. If omitted 0 (zero) is used.

3. Example 1

These examples truncate all numbers to 0 (zero) decimals, in other words all decimal values are filtered out leaving only integers.

The first example has the source value in cell B3 and the TRUNC result is in cell C3. The value is -19 and the truncated value is also -19. The source value has no decimals.

Formula in cell C3:

The second example value is in cell B4 and the TRUNC result is in cell C4. The value is 0.9 and the truncated value is 0 (zero), the decimal is left out leaving only 0 (zero) as the result. The source value has 1 decimal.

The third value is in cell B5 and the TRUNC result is in cell C5. The value is -2.029 and the truncated value is -2, the decimals are left out leaving only -2 as the result. The source value has 3 decimals.

The fifth value is in cell B6 and the TRUNC result is in cell C6. The value is -0.9 and the truncated value is 0, the decimal is left out leaving only 0 (zero) as the result. The source value has 1 decimal.

The fourth value is in cell B7 and the TRUNC result is in cell C7. The value is 39.5 and the truncated value is 39, the decimal is left out leaving only 39 as the result. The source value has 1 decimal.

The sixth value is in cell B8 and the TRUNC result is in cell C8. The value is 21.2 and the truncated value is 21, the decimal is left out leaving only 0 (zero) as the result. The source value has 1 decimal.

The seventh value is in cell B9 and the TRUNC result is in cell C9. The value is 0.0035 and the truncated value is 0, the decimals are left out leaving only 0 (zero) as the result. The source value has 4 decimals.

The eigth value is in cell B10 and the TRUNC result is in cell C10. The value is 3.6 and the truncated value is 3, the decimal is left out leaving only 3 as the result. The source value has 1 decimal.

4. Example 2

A vehicle drives from location A to location B. The journey takes 47 minutes, and the car maintains an average speed of 62 miles per hour. What is the distance between points A and B? Truncate the result to one decimal?

What we know:

• The distance is equal to speed x time.
• Speed = 60 miles per hour
• Time = 47 minutes

Formula in cell C22:

The formula in cell C22 returns 48.5 miles which represents the distance between point A to point B based on a constant speed of 60 miles / hour over a duration of 47 minutes.

Lets calculate this manually:

1. Convert time from minutes to hours. 47 minutes / 60 minutes = 47/60 hours
2. Multiply duration by speed. 47/60 hours * 62 miles/hour = 47*62/60 miles = 48.5666666666667 miles.
3. Truncate to one decimal: 48.5666666666667 = 48.5 miles.

5. Example 3

An object above ground has initial velocity of 2 feet/s. The final velocity right before ground impact is 4 feet/s. The time it takes to reach the ground is 1.3 seconds. What is the acceleration? Truncate the answer to 2 decimals.

What we know:

• Basic acceleration formula: a = (v - u) / t
  a = acceleration, v = final velocity, u = initial velocity, t = time
• Acceleration: Unknown
• Initial velocity: 2 feet/s
• Final velocity: 4 feet/s
• Time: 1.3 seconds

Formula in cell C23:

The formula in cell C22 returns 1.53 feet/s² which represents the acceleration with an initial velocity of 2 feet/s and a final velocity of 4 feet/s based on a duration of 1.3 seconds.

Lets calculate this manually:

1. Final velocity minus the initial velocity: 4-2 = 2
2. Ratio between the velocity difference and the duration: 2/1.3 = 1.53846153846154
3. Truncate the result to two decimals: 1.53846153846154 = 1.53 feet/s²

This result is equal to the value in cell C23.

6. Function not working

The TRUNC function returns

• #VALUE! error if you use a non-numeric input value.
• #NAME? error if you misspell the function name.
• propagates errors, meaning that if the input contains an error (e.g., #VALUE!, #REF!), the function will return the same error.

6.1 Troubleshooting the error value

When you encounter an error value in a cell a warning symbol appears, displayed in the image above. Press with mouse on it to see a pop-up menu that lets you get more information about the error.

1. The first line describes the error if you press with left mouse button on it.
2. The second line opens a pane that explains the error in greater detail.
3. The third line takes you to the "Evaluate Formula" tool, a dialog box appears allowing you to examine the formula in greater detail.
4. This line lets you ignore the error value meaning the warning icon disappears, however, the error is still in the cell.
5. The fifth line lets you edit the formula in the Formula bar.
6. The sixth line opens the Excel settings so you can adjust the Error Checking Options.

Here are a few of the most common Excel errors you may encounter.

#NULL error - This error occurs most often if you by mistake use a space character in a formula where it shouldn't be. Excel interprets a space character as an intersection operator. If the ranges don't intersect an #NULL error is returned. The #NULL! error occurs when a formula attempts to calculate the intersection of two ranges that do not actually intersect. This can happen when the wrong range operator is used in the formula, or when the intersection operator (represented by a space character) is used between two ranges that do not overlap. To fix this error double check that the ranges referenced in the formula that use the intersection operator actually have cells in common.

#SPILL error - The #SPILL! error occurs only in version Excel 365 and is caused by a dynamic array being to large, meaning there are cells below and/or to the right that are not empty. This prevents the dynamic array formula expanding into new empty cells.

#DIV/0 error - This error happens if you try to divide a number by 0 (zero) or a value that equates to zero which is not possible mathematically.

#VALUE error - The #VALUE error occurs when a formula has a value that is of the wrong data type. Such as text where a number is expected or when dates are evaluated as text.

#REF error - The #REF error happens when a cell reference is invalid. This can happen if a cell is deleted that is referenced by a formula.

#NAME error - The #NAME error happens if you misspelled a function or a named range.

#NUM error - The #NUM error shows up when you try to use invalid numeric values in formulas, like square root of a negative number.

#N/A error - The #N/A error happens when a value is not available for a formula or found in a given cell range, for example in the VLOOKUP or MATCH functions.

#GETTING_DATA error - The #GETTING_DATA error shows while external sources are loading, this can indicate a delay in fetching the data or that the external source is unavailable right now.

6.2 The formula returns an unexpected value

To understand why a formula returns an unexpected value we need to examine the calculations steps in detail. Luckily, Excel has a tool that is really handy in these situations. Here is how to troubleshoot a formula:

1. Select the cell containing the formula you want to examine in detail.
2. Go to tab “Formulas” on the ribbon.
3. Press with left mouse button on "Evaluate Formula" button. A dialog box appears.
   The formula appears in a white field inside the dialog box. Underlined expressions are calculations being processed in the next step. The italicized expression is the most recent result. The buttons at the bottom of the dialog box allows you to evaluate the formula in smaller calculations which you control.
4. Press with left mouse button on the "Evaluate" button located at the bottom of the dialog box to process the underlined expression.
5. Repeat pressing the "Evaluate" button until you have seen all calculations step by step. This allows you to examine the formula in greater detail and hopefully find the culprit.
6. Press "Close" button to dismiss the dialog box.

There is also another way to debug formulas using the function key F9. F9 is especially useful if you have a feeling that a specific part of the formula is the issue, this makes it faster than the "Evaluate Formula" tool since you don't need to go through all calculations to find the issue..

1. Enter Edit mode: Double-press with left mouse button on the cell or press F2 to enter Edit mode for the formula.
2. Select part of the formula: Highlight the specific part of the formula you want to evaluate. You can select and evaluate any part of the formula that could work as a standalone formula.
3. Press F9: This will calculate and display the result of just that selected portion.
4. Evaluate step-by-step: You can select and evaluate different parts of the formula to see intermediate results.
5. Check for errors: This allows you to pinpoint which part of a complex formula may be causing an error.

The image above shows cell reference B3 converted to hard-coded value using the F9 key. The TRUNC function requires numerical values which is not the case in this example. We have found what is wrong with the formula.

Tips!

• View actual values: Selecting a cell reference and pressing F9 will show the actual values in those cells.
• Exit safely: Press Esc to exit Edit mode without changing the formula. Don't press Enter, as that would replace the formula part with the calculated value.
• Full recalculation: Pressing F9 outside of Edit mode will recalculate all formulas in the workbook.

Remember to be careful not to accidentally overwrite parts of your formula when using F9. Always exit with Esc rather than Enter to preserve the original formula. However, if you make a mistake overwriting the formula it is not the end of the world. You can “undo” the action by pressing keyboard shortcut keys CTRL + z or pressing the “Undo” button

6.3 Other errors

Floating-point arithmetic may give inaccurate results in Excel - Article

Floating-point errors are usually very small, often beyond the 15th decimal place, and in most cases don't affect calculations significantly.

Functions in 'Math and trigonometry' category

The TRUNC function function is one of 62 functions in the 'Math and trigonometry' category.

Excel function categories

Excel categories

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