A regular 12month average reduces a year of monthly figures into a single average number. A 12month rolling average, or moving average, is simply a series of 12month averages over multiple consecutive 12month periods. This statistical tool can help you gauge the overall direction of a series of monthly data, because it smoothes out the effects of monthtomonth changes. You can use a 12month rolling average to analyze almost any type of monthly numbers, such as revenues, profits, stock prices or account balances.
Step 1
Gather the monthly data for which you want to calculate a 12month rolling average. You need at least 13 consecutive months of information, but the more you have, the more useful the rolling average will be.
For example, assume you want to calculate a 12month rolling average for the following 14 months of sales:
 January 2017: $50,000
 February 2017: $55,000
 March 2017: $60,000
 April 2017: $65,000
 May 2017: $70,000
 June 2017: $75,000
 July 2017: $72,000
 August 2017: $70,000
 September 2017: $68,000
 October 2017: $71,000
 November 2017: $76,000
 December 2017: $85,000
 January 2018: $73,000
 February 2018: $67,000
Step 2
Add the monthly values of the oldest 12month period.
In the example, add the monthly sales figures from January through December 2017:
$50,000 + $55,000 + $60,000 + $65,000 + $70,000 + $75,000 + $72,000 + $70,000 + $68,000 + $71,000 + $76,000 + $85,000 = $817,000
Step 3
Divide your result by 12 to calculate the average monthly figure for the oldest 12month period. This represents the first rolling average.
In this example, divide $817,000 by 12:
$817,000 / 12 months = $68,083 for the first rolling average
Step 4
Add the monthly figures for the next consecutive 12month period. This includes the previous 12month period except the oldest month. It also includes the newest month immediately following the previous 12month period.
In the example, the next consecutive 12month period is February 2017 through January 2018. Add the monthly sales numbers to get $840,000.
Step 5
Divide your result by 12 to calculate the second rolling average. In the example, divide $840,000 by 12:
$840,000 / 12 = $70,000 second rolling average
Step 6
Add the monthly data for the next consecutive 12month period, and divide your result by 12 to calculate the third rolling average. Repeat the same calculation for each subsequent 12month period to calculate the remaining rolling averages.
In the example, add the monthly sales from March 2017 through February 2018 to get $852,000. Divide $852,000 by 12 to get a third moving average of $71,000.
The 12month rolling averages are $68,083, $70,000 and $71,000, which shows an increasing sales trend over the given period.
Tip

 Plot your monthly figures and 12month rolling average on a graph to see the trend of your data.