Definition: Year-on-Year [YoY]

Year-on-Year (or YoY) means comparing data from a date range in one year to the same date range in the previous year.

For example, you could say “In March we had year on year revenue growth of 20%” which would mean that March of this year had 20% more revenue than March in the year before.



Year-on-Year Formula

Use this equation to calculate the percentage change in a metric from one year compared to the same period in the previous year.


An image showing the equation for calculating Year-on-Year changes in stats. The equation is: Year-on-Year Change = ((Any Metric ÷ Same Metric from the previous year) -1) x100Click to enlarge

Year-on-Year Change =
((Any Metric ÷ Same Metric from the previous year) -1) x100 


Alternative Equations

The Year-on-Year calculation we have provided is the most convenient to use, especially on a calculator. However, there are other ways to calculate Year-on-Year changes. They all come out with the same answer, but you input them in different ways.

The most commonly used Year-on-Year calculation is:

((This Year – Previous Year) ÷ Previous Year) x100 

I personally don’t like this equation so much as if you are using a calculator then you have to input the second number twice.

If you want to work out a Year-on-Year change in Excel, then the equation is even simpler:


The formula for calculating Year-on-Year changes in excel is shown

(Any Metric ÷ Same Metric from the previous year) -100%


This only works because Excel will turn this calculation into a percentage automatically. If you did this same calculation in a calculator you would get 0.


Different ways to compare Year-on-Year performance

In most cases simply comparing how something did this year to the same dates last year will give you a reasonable view of how you are doing. However, there are a few variations on this idea that are worth knowing about.


Day Shifted Year-on-Year

For many organisations weekend and weekdays perform very differently. B2B organisations, for example, are likely to have a much higher volume of business during the typical 9-5 Monday to Friday workweek than on weekends.

Because of this, it can be useful to take into account the number of weekdays and weekend days that are in any date range. If you are comparing a number of days that is a multiple of 7 then that won’t be a problem as you will have the same number of weekdays and weekend days no matter which date range you choose.

For other lengths of comparison, this might cause a problem. The standard solution when comparing Year-on-Year is to simply shift the date range along by a few days so they start on the same day of the week.

So if your start date is the first Monday in February this year, then make the start date of your comparison the first Monday of February last year. Make sure to change the end dates too so that the comparisons are of the same length of time.


Relative to start comparisons

Some organisations have different run dates for an event every year – but the event still runs for the same length of time.

When this is the case, a simple Year-on-Year comparison might not make sense. For example, this year a marketing campaign started a few weeks early. Therefore if you compare it directly Year-on-Year this years campaign will have been running for longer.

Even if you just compare the previous week, digital marketing gets optimised over time so you can’t compare results of week 3 of a campaign directly to results from week 1.

To fix this problem you compare dates since the start date. That is, if your event started  February 1st this year, and March 3rd last year then you consider both those dates as “Day 1”. Then February 2nd this year is “Day 2” (as is March 4th last year), February 3rd is “Day 3” (as is March 5th last year), and so on.

You label each day of the event with Day 1, Day 2, Day 3 etc, and then compare like-for-like. Day 1 this year versus Day 1 last year (or Week 1 this year versus Week 1 last year) etc.

This sort of Year-on-Year comparison takes a bit more work, but is a much fairer way to examine many events.


Year-To-Date (YTD) comparisons

Year-To-Date simply means this year so far. If it is August 6th, then YTD is January 1st to August 6th.

When comparing a whole year to the previous year, it generally makes sense to run a YTD comparison. By this I mean, again if it’s August 6th then you compare January 1st to August 6th this year, with January 1st to August 6th last year.

This way you are comparing the same amount of days. It’s an easy to understand comparison – and it’s also interesting as you can watch it unfold.

By checking on your YoY Year-To-Date stats regularly you can see if you are going to beat last years results in more or less real-time. It’s rare that stats are fun, but this gets close.


Other names for Year-on-Year (synonyms)

  • Year On Year
  • Year Over Year


Find out more

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