Belron's online customer experience manager Craig Sullivan gave a great presentation at last week's Online Marketing Masterclasses event, and one of the many nuggets contained within was that strict postcode validation was causing 2.5% of customers to abandon.

The problem that Craig discovered was that customers were entering the letter 'O' when a zero was required, triggering an error message. Since they may have been unaware of their mistake, this frustration was causing customers to abandon.

To get around this, the forms now anticipate these errors so that users would continue through the form, not even knowing they had made a mistake, an elegant solution to the problem.

It really should be something that every online retailer should do in its registration or checkout process, so I've been checking some of the better known UK etailers to see how they handle this error.

Retailers that fail the postcode test are:





The retailer does at least attempt to instruct customers to enter the postcode in the correct format, but doesn't anticipate this particular input error:

I could show you more screenshots, but suffice to say, eight of the ten e-commerce websites I tried this on produced an error when I entered the letter 'O' when a zero was called for. The others were Comet, John Lewis, M&S, and ASOS.

Those that passed the postcode test were HMV and, both of which simply ignore the error and allow users to continue, thus removing a potential source of friction.

There are other issues with form entry on e-commerce sites where strict validation can cause errors for customers, and the key is to test for the common errors that are causing abandonment and make forms flexible enough to deal with these issues.

Currys, John Lewis and the other sites which produce errors when customers enter postcodes like this should look at their analytics to see if this issue is affecting them. If so, this one change to postcode entry could an easy, quick way to reduce abandonment rates.

Graham Charlton

Published 25 November, 2009 by Graham Charlton

Graham Charlton is the former Editor-in-Chief at Econsultancy. Follow him on Twitter or connect via Linkedin or Google+

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Comments (9)

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Good point.  The "0" or "O" and "1","I" and "l" problems are even bigger with CAPTCHA.  The CAPTCHA on our site has an x or check mark to let the user know if it's right and a refresh option if the text is not readable. 

over 8 years ago


Lindsey Annison, Web PR Consultant at Clickthrough Marketing

There are so many issues with forms. There are still far too many etailers who force users to reload the page when an error is spotted, and fill out all the fields again. Result? Instant abandonment.

Entering mobile numbers is another, where for instance +44 is required and many users enter the 0 after that causing an error.

I still see forms where the T&Cs open in the same page instead of a new window. As the T&Cs are generally at the end of the form, this can cause problems if the user has already completed the form.

Not clearly marking required fields is another. Or, if a field is required, explaining exactly why your inside leg measurement is needed for your subscription to a magazine.

Or when the isn't configured properly and the error page doesn't tell you how to inform the webmaster or what to do instead. I always wonder how many sales and enquiries this may have lost the company, and tend to find a contact address to email them to inform them. I have never had a single reply over the years to my emails, but I have noticed the problem has been fixed on many occasions.

There is an easy way to test forms. Grab a couple of kids - the holidays are coming up and they all want a few quid - and tell them to find all the ways they can to stop the form working. Cheap, imaginative and very effective testers, our next generation.

over 8 years ago

Graham Charlton

Graham Charlton, Editor in Chief at ClickZ Global

Good point Christopher, hadn't considered CAPTCHA.

@Lindsey - I think there are plenty of issues that may seem relatively minor with web forms, but that can have a significant impact on abandonment rates.

All the things you mention are annoying for users, though making people fill out the form again is particularly bad.

over 8 years ago


Lindsey Annison, Web PR Consultant at Clickthrough Marketing

That last is still ongoing too.

Check out the blog post on here about the new Whistles site from 10th Nov

"Forms were easy enough to fill in, but in the case of errors, users have to re-enter all of the details they have entered."

over 8 years ago



Other annoyances with postcodes in forms are things like:

1) Insisting on the space between the two parts, or conversely insisting on no space between the two parts

2) Informational sites where I am looking for something in my region but it will only accept a full post code, not just the first three letters and numbers.

And don't get me onto credit card numbers. If I want to put spaces between each block of four digits it's a fairly trivial bit of coding to remove those and process the number correctly, but most sites insist on no spaces between the numbers which apart from being irritating makes it more likely that I will get the number wrong.

over 8 years ago


Craig Sullivan, Customer Experience Manager at Belron International


Great to see a topic on one of my fave subjects that I aired last week.  The validation issues I come across include dates, postcodes, phone numbers, credit cards, start/end dates and many others...

I think people are incredibly lax about instrumenting their e-commerce platform or adding analytics insight for forms issues.  There is a serious amount of money being lost because some website owners either (a) Don't know they have these problems (b) Know they are there but not the extent or (c) Measure them but haven't fixed them.  

In the postcode example, the issues I came across were:

O and 0 interchanged

1 and l interchanged

Failure to accept space/one space/two spaces/no space in postcode.

Shifted characters (i.e. £ instead of 3, $ rather than 4)

Transpositional errors (items swapped in the postcode eg. c0r rather than cr0)

The shift issue is an interesting one because a whole group of people put their postcodes in using CAPS.  This means all the numbers get shifted and hence a load of validtion to sort out.

The solution to the postcode issue is to at least find out what the common validation errors are for your site - they may differ incredibly from mine.  Once you know what they are, you can correct them.

So in the examples above, what we do is use the nicely specified post office incode and outcode rules (

You can then (in most cases) figure out what the user actually meant.  If there is ambiguity (in other words, they might mean one of two things) then you don't correct the field.  If you 'know' what they were asking for, just go ahead and process the data.

The classic example (and yes, I still find sites) is the credit card field that won't accept spaces, dashes, dots or other formatting.  Sheesh - its just a number that might need cleaning.  One common issue I've found in logs is that the credit card number doesn't match the 'type' of card selected by the user.  Again, you can 'decide' that the card is a visa if you know the number.  Is this such a hard thing to fix if it makes you money?

Anyway, my rant is over - I'd love to write an article on data validation for e-consultancy with some good examples but for now, I'll leave you with this - the bible for forms interactions/errors/validation/messaging: 

Luke Wroblewski - Filling in the blanks :

Additional Luke W resources:

over 8 years ago


Jim Williams

Hi there,

Postcode Anywhere has been offering this more subtle functionality for years. It auto-corrects postcodes for exactly this problem:

Out of interest, if anyone has any address entry gripes that aren't satisfied don't hesitate to drop me a line via my blog. The PCA team are always eager to hear how better functionality can be integrated.


over 8 years ago


Norman Rhoads

I have my american credit cards sent to my address in Italy so that when I try to enter my post code for purchases based in the U.K. it rejects my Italian post code as invalid. I need to do business with Sky television but it will not accept my Italian post code. Can I get around this?

Norman Rhoads 

over 8 years ago



I have had a similar problem to this except it is not the postcode that is incorrect. I recently moved into a brand new student hall of residence in Bradford and I wanted to change my address on, but my postcode is apparrently invalid. I think that because its brand new, the postcode hasnt been registered yet. I have been tempted to put in the university postcode instead as it is right next to the accommodation but I am wondering if the the postman will realise it is not The University it needs to go to

over 6 years ago

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