# How often do postcodes change?

Whenever I'm doing a refresh of our postcode data I find it interesting to look at what's changed in the data over the last three months. I'd always thought that the data would be fairly stable, but it turns out that the Royal Mail chop and change them surprisingly often.

Here's a graph of the number of postcode units introduced and terminated each month over the last decade.

Apart from the notable peaks in February 2006 and June 2008, the number terminated (made inactive and no longer officially recognised) tends to hover between 0 and 4000. The average over the decade works out to be 2561 terminations each month.

The number of introductions is similar and slightly more consistent, with an average of 2754 each month.

If we add these figures up over the course of a year, it turns out that the Royal Mail make around 63,780 changes every 12 months. Assuming there is a total of 1.75 million active units, that's a turnover rate of 3.65% per year.

## How many are there?

Now that we have the number of introductions and terminations each month, it's easy to work backwards and figure out how the total number of active units has changed over time.

We can see that throughout the previous decade there was a consistent growth in the total number of live postcodes, punctuated by the two major consolidation events in 2006 and 2008. However since 2008 the Royal Mail has kept the total number at around 1.75 million, with a slow and steady consolidation over the past two years.

Written by Alex Edwards |