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The DATEDIF function calculates the number of periods between two dates. The best way to remember this function is it calculates the DATE DIFference between two dates. What is DATEDIF? The DATEDIF function is a popular formula that has 3 parameters which are all required. If you encounter any error when using this function check you have populated all three fields correctly. The function reference is as follows: =DATEDIF(start_date, end_date, unit) The start_date parameter should be the earliest date, the end_date being the latest date, and the unit is the value of the periods you want returned from the difference between those two dates. Accepted values in Google Sheets for the unit value are: Date Difference in Days By setting the third parameter to the DATEDIF formula to D it means the resulting value returned will calculate the number of days between the two dates. Here are some examples: ABCD11 June 20201 June 2020=DATEDIF(A1, B1, "D")021 June 20202 June 2020=DATEDIF(A2, B2, "D")131 June 202031 May 2020=DATEDIF(A3, B3, "D")#NUM! Several things to note about these tests when using the DATEDIF function and the unit parameter as D: The dates are not inclusive. Notice the first row is 0, if it were inclusive it would have been 1.Should the end_date come before the start_date you will get an #NUM! error. Make sure your end_date occurs on or after the start_date. Date Difference in Months If you want to calculate the difference between two dates in months, then set the third parameter of the formula to "M", here are some interesting examples of what this looks like for certain values: ABCD129 February 202029 February 2020=DATEDIF(A1, B1, "M")0229 February 202028 March 2020=DATEDIF(A2, B2, "M")0329 February 202029 March 2020=DATEDIF(A3, B3, "M")1429 February 20201 March 2021=DATEDIF(A4, B4, "M")12531 January 202029 February 2020=DATEDIF(A5, B5, "M")0631 January 20201 March 2020=DATEDIF(A6, B6, "M")1 As can be seen from the table above, the day of the month needs to be either eclipsed or matched for the returning value to increment. In rows 5 and 6 especially we can see the days in the month of February 2020 would not have eclipsed the start_date of 31st January 2020, but when the end_date advances into the next month (1st March) the increment occurs. Therefore, if your start_date is the end of a month containing 31 days it will not be until the 1st day of the following month, preceding a month containing only 28, 29 or 30 days, that the value will be incremented. Date Difference in Years If you want to calculate the difference between two dates as years then set the third parameter value to "Y". Here is what this would look like based on the following inputs: ABCD129 February 202029 February 2020=DATEDIF(A1, B1, "Y")0229 February 202028 February 2021=DATEDIF(A2, B2, "Y")0328 February 202028 February 2021=DATEDIF(A3, B3, "Y")1429 February 20201 March 2021=DATEDIF(A4, B4, "Y")1 As can be seen from the examples above, it's not until the date and month of the start_date has been eclipsed or matched the value returned by the DATEDIF formula increments. This is very similar to when calculating the date difference in months. Date Difference in Days Irrespective of Months If you need to calculate the difference in days between two dates irrespective of the difference between months then you'll need to use "MD" as the value of the third parameter, as demonstrated below: ABCD131 January 202031 January 2020=DATEDIF(A1, B1, "MD")0231 January 202029 February 2020=DATEDIF(A2, B2, "MD")29331 January 20201 March 2020=DATEDIF(A3, B3, "MD")-1431 January 20202 March 2020=DATEDIF(A4, B4, "MD")0531 January 202030 March 2020=DATEDIF(A5, B5, "MD")27631 January 202031 March 2020=DATEDIF(A6, B6, "MD")0731 January 20201 April 2020=DATEDIF(A7, B7, "MD")1 As previously noted with the difference in days we can see from the examples above the difference in days is not inclusive. However, there are some interesting results: Row 3 shows a result of -1. Why? This implies there was a day short in the previous month of getting to the same date, and the current date of 1st March 2020 is 1 day short of the 31 days (29 days in February + 1 day in March = 30 days - 31 days = -1). This then puts the remaining values of that month (in March) out, until we hit the new month April. Date Difference in Whole Months If you want to calculate the difference between two dates in whole months you can set the third parameter to the DATEDIF formula to "YM". ABCD131 January 202031 January 2020=DATEDIF(A1, B1, "YM")0231 January 202029 February 2020=DATEDIF(A2, B2, "YM")0331 January 20201 March 2020=DATEDIF(A3, B3, "YM")1431 January 202031 March 2020=DATEDIF(A4, B4, "YM")2 The results from this result set above are fairly simple to understand and are consistent with what we already know about - the day of the month needs to be matched or eclipsed to increment the value. Date Difference in Days Irrespective of Years Similar to our previous example with date differences in days irrespective of months we have a similar calculation but this time irrespective of years, here are some examples: ABCD129 February 202029 February 2020=DATEDIF(A1, B1, "YD")0229 February 202028 February 2021=DATEDIF(A2, B2, "YM")365329 February 20201 March 2020=DATEDIF(A3, B3, "YM")0 Consistent with the days difference irrespective of months we see that where the start date isn't matched by day of month and month, it calculates the difference the previous month fell short. Benefits of DATEDIF Over Subtracting Two Dates An objection to using the DATEDIF formula is that it achieves the same result when subtracting dates, which is certainly far simpler than trying to remember a formula, and it's parameter values. The biggest benefit of the DATEDIF formula is that it helps to calculate the difference between two dates by providing us with the type difference we need. Therefore, the DATEDIF formula is more versatile for various use cases. Another minor benefit to using the DATEDIF function when calculating the difference in days between two dates over the simple subtraction method is if the input dates contain time. ABCD11 June 202011 December 2020=B1-A119321 June 202011 December 2020=DATEDIF(A2, B2, "D")19331 June 2020 8:00:0011 December 2020 10:00:00=B3-A3193.08333341 June 2020 8:00:0011 December 2020 10:00:00=DATEDIF(A4, B4, "D")193 You can still achieve the same answer as the DATEDIF function, but you would need to remember and apply to use the TRUNC formula to achieve the same answer in row 3 above, like so: ABCD51 June 2020 8:00:0011 December 2020 10:00:00=TRUNC(B5-A5)193 DATEDIF Errors and Problems There are a couple of things to be mindful of when using the DATEDIF function. As already shown above in the DATEDIF days examples we had a result on the last row that gave us an error. If you do get a #NUM! error check the parameter values are correct, and the earliest date is the start_date value, and the later date is the end_date value. Provided your parameter values have been set correctly, the only other type of error which may cause problems and may not be as obvious is if the locale setting of your dates are not what you anticipated. Incorrect DATEDIF Locale If you're getting an answer which definitely isn't correct you will want to check the settings of your spreadsheet to ensure it correctly interprets a date field value. For example, some countries, such as the UK and Australia, have dates set to the following format: DD/MM/YYYY whereas other countries, such as Canada and the Unites States, have date values set to the format of: MM/DD/YYYY. ABCD101/06/202011/12/2020=DATEDIF(A1, B1, "D")193 for DD/MM/YYYY folks, or 311 for MM/DD/YYYY folks! Ways to minimise this error occurring would be to quickly check your locale settings are correct before starting a new spreadsheet, or when modifying a spreadsheet. In a Google Sheet this would be simply going to File > Spreadsheet Settings > Locale - change this to your country. Check Google Sheets locale settings if you’re getting weird answers Another way to check is to input a date that wouldn't be a date in the other format, for example, try 01/13/2020 and 13/01/2020 - one of these will not work and your DATEDIF formula will return a #VALUE! error as the date fields entered aren't actual dates. Conclusion In this article we've done a deep dive into the DATEDIF formula and seen the results it provided based on different parameter values. We've also seen how the formula can be better suited than simply subtracting two dates, and we've diagnosed our problems and fixed them. Overall the DATEDIF function is a fantastic function to use, and you should look at incorporating it more in your own daily use. If you'd like to learn more about the function in Google Sheets, you can read the documentation.