# Finding Leap Years in Tableau – 3 Methods

###### Blog | June 21, 2018 | By Vijai Narasimha

Leap year! Good that we get to see Feb 29. Also special for people born on Feb 29 because they get to celebrate. This blog is going to be simpler than many of the other examples we have tried before.

We have heard many stories. One of them dates back to the Roman civilization where each emperor created a month credited to his name based on the harvesting seasons and started adding extra days etc. etc. and the story continues.

For some firms, accounting the extra day can have its own positive and negative impact. There are few companies like Food management, Delivery services, Catering services and small departments within such companies that allocate budget on a day to day basis. For them, the extra day can become an issue. For some financial companies, it works well as it generates an extra day of revenue. In some blogs and books, the theme has recurred as “How to account for Financial Distortions with extra Dates?”

When it comes to reporting, most us observe some peculiar values when doing a Year over Year or Month over Month or Week over Week comparison involving a Leap year. We don’t realize it in the beginning. We dig deeper and investigate the data and then we find the leap.

Also, in some cases, end users ask for some indicator or a simple note to identify the leap years. In some situations, end users request for a leap year filter too.

In this blog, we will discuss 3 very simple methods to identify if a year is a Leap year. There are three basic things that come to mind when we think about a Leap Year. First being that leap year occurs once in 4 years; the second being February 29 and the third will be the famous 366 days. So, our methods will be based on these facts.

Some of us might think that it is so easy to just google all the leap years and put it into tableau. It would be such a waste of time to go through all calculations. That is all true. But the idea here is to explore and leverage Tableau’s features to suit our needs.

Unfortunately, it is not as easy as Excel to find Leap years. Some excel users have tried some complex mod functions, some of them have tried test of divisibility etc. We shall use some of the same concepts but using Tableau’s features.

For this example, a simple data file consisting of 10 full years is prepared. Every day of every month of every year from 2011 to 2020.

From this data we are interested to find these dates.

Using the same data in Tableau.

**Method 1**

This is the easiest and the simplest method to find a leap year. If we briefly study the history of leap years, we can see that it occurs perfectly on the 4th year in a series starting from 1753 (first leap year was 1752), it is always an even number and it is always divisible by 4. Many of us did not know that. That is all we needed. We got our solution!

1) First, we need to isolate only the year from the Date field. This will now have a number data type which can be used for mathematical calculations

2) At this point, Tableau will treat it as a measure since it is a number data type. We need to convert it to a Dimension but retain the Number data type.

3) Now, for the simple calculation. We can approach in two ways. We can divide by 4 and confirm if the number is an integer. If it is a float that means, it is not completely divisible by 4. Or, we can take the modulus approach with % mathematical operator. This will find the integer remainder (Value remaining after the division) For example: We want to divide 10 by 3. As integer division, the quotient is 3 and remainder is 1 because 10 is not completely divisible by 3. So, the % operator provides the answer 1. If the value is 0, then it is completely divisible.

Again, Tableau will treat it as a Measure, but we need to convert it to Dimension. Not a must. It would be easy to debug later. Using as a Discrete field on rows.

4) We have the answer here. But the last step would be a conditional step to identify as a Flag.

** Caution: 1800, 1900, 2100, 2200, 2300 are not leap years though divisible by 4 ** as pointed out by Srini Ramanathan! Thanks Srini.

**Method 2**

This is a slightly higher method of solving this question. Here we will focus on February 29. So, our concept says that, if a year consists of Feb 29, then that will be a leap year.

1) Again, like the previous method, we need to isolate only the year based on the required condition. Here we need an AND condition because we need to check for the month and the day.

This Calculation will only pick that particular day (row) where February 29 is found. Rest of them will be Null.

The field will be under measures. We need to convert it to a Dimension and use it on the view.

Though we have the answer here, when reporting the Null for every other date in that year will cause an issue. So, we need to repair by getting rid of all the Nulls in that year.

3) We can try this in multiple ways. But, here we are using a simple Fixed function i.e. for every year, we need to tell Tableau to only look at the number and not the Null. Minimum or Maximum function will work in this case.

Again, this will be a Measure. We need to convert to a Dimension and use on the view.

4) The last step would be to provide a conditional flag for leap year.

**Method 3**

Now coming to a situation where February 29 is not available in the reporting data. May be the date was deliberately eliminated or no data was recorded on that date. For such a scenario, we cannot use Method 2 as any year which does not have that date will be treated as Null. Method 1 will work for sure in all cases. But for this scenario, we will use the number of days to find the leap year.

1) First step would be to create a Calculation to identify the first day of each year i.e. January 1. We can do it either by creating our own Date or using the DateTrunc function.

2) Similar to the first step, we need to find the last day of the year. We can use a DateTrunc function and subtract by one day. But it is easier to create the date for December 31.

3) The next step would be to find the number of days in each year. Here we need to subtract the two first day from the last day. But we need to remember to add an extra day as the first day is already Day number 1. Ideally, we need to subtract using the last day of the previous year. But it is easy to just add 1.

Again, this will be a Measure. We need to convert to a Dimension and use on the view.

4) The last step would be to provide a conditional flag for leap year based on number of days.