A number of well-known retailers are making basic mistakes with postcode validation which could be increasing their checkout abandonment rates. 

Users are prone to make errors when completing web forms, and anticipating and dealing with common errors can minimise the risk that user frustration will lead to them abandoning the checkout. 

I’ll look at one common error, which many sites fail to account for. An oversight which may be increasing their checkout abandonment rates… 

The postcode validation problem 

There are a number of issues around postcode entry, such as whether sites accept postcodes with or without a space in the middle (they should accept either). 

For example, if you enter your postcode without spaces on Tesco Clothing, you get an error message insisting on spacing and capitals.

Why not tell customers this before they type? 


Update: March 2013 – Venda and Tesco have improved the validation on the postcode field and this is no longer an issue.

Another, more subtle error is that of customers entering zero instead of the letter ‘O’, or the number ‘1’ instead of the letter ‘i’ and vice versa. 

Since it’s an error which isn’t always noticed by customers, and error messaging on sites is frequently unclear, users are likely to repeat it, becoming more frustrated with each error message.

The likely result, unless they realise their mistake, is that they will abandon the purchase.

In the case of Belron, Craig Sullivan found that this was causing 2.5% of customers to abandon. To solve the problem, Belron’s forms now anticipates these errors so that users continue through the form, not even knowing they had made a mistake. 

This avoids the risk that customers will abandon, and also means that no annoying error messages are necessary. 

However, while the potential solution is simple, many big name retailers are still failing this test. In this case, I’ve used Econsultancy’s postcode, replacing the 1 with the letter ‘i’. 

Retailers that fail the postcode test


Here, entering ‘i’ instead of the number 1 produces an error message, which does nothing at all to deal with the problem. If the user doesn’t happen to spot their error, they are at a dead-end. 



Same problem on Tesco. The error message is less confusing than that on Argos, though still doesn’t help. 


I get the same problem on Amazon… 



The error message is pretty useless. 


The postcode error trips up ASOS. It does suggest some alternative steps at least, but it’s a complicated process, especially when it could just anticipate the error. 

John Lewis

John Lewis won’t accept my postcode: 

However, it does provide a ‘don’t know the postcode?’ link, which enables me to enter the adresss before it suggests possible codes. This solution at least avoids leaving the customer at a dead end. 

Who is getting this right? 


Kudos to Play.com, which accepts my error without mentioning it, and displays a list of possible addresses:  


M&S sort of gets it right. It doesn’t produce an error message but instead lets the user continue with the incorrect postcode. I guess it would be close enough to get to the right destination. 


So, just one of the top ten UK retailers are anticipating and dealing with this error, though M&S at least provides an alternative approach which may minimise the risk of the customer abandoning the checkout. 

If, for the sake of argument, a similar proportion of users are being tripped up by the error as Craig Sullivan reported for Belron (though this was a few years ago), then this represents a massive loss of potential revenue when we look at online giants like Argos and Amazon. 

These retailers would be wise to study their analytics and run some tests to see if strict postcode validation for this and other errors is a problem. If it is, the solution is simple…