How often should you redesign a ecommerce site?

What is the general rule of thumb for ecommerce websites to redesign total look, navigation and features for the website?

My current understanding is to freshing the site with new features and small changes every 3-4 months with major redesign of website every year.

Is this close to accurate and what is reason for total redesign and how do you do this with minimal impact on SE rankings?

[rustybrick]

You should constantly be tweaking the design to squeeze out higher and higher conversions. Complete redesigns are not needed every 3 - 4 months. It depends on your goals and your metrics.

[vayapues]

In someways my comments won't apply, since I do very little in the way of ecommerce. However, the operation of my sites still takes conversion and 'calls to action' into consideration, so I believe there is at least some merit.

Firstly, I agree with Rustybrick. You should constantly be tweaking your sites. Really, on a daily basis. People change, trends change, products change, effective color schemes change, tastes change, etc.

What works today will not work tomorrow.

Bare in mind that my audience is firstly, primarily made up of children, and secondly, that they return to my site often. For these reasons I update the designs of my sites about once every year. This helps to keep it fresh and exciting for them. Otherwise I see a dip in my traffic. I introduce new games and activities every month or so as well.

The issue for my audience is two-fold. 1. Keep them from getting bored. and 2. Try to keep my finger on the pulse of what my audience is currently responding to, or in other words, what will make them convert.

[MattUK]

It's hard to give a definitive answer. Web design seems to be like fashion and seems to have cycles. You can tell pretty easily if a site is looking tired and dated. There seem to be a lot of sites updating at the moment driven by the Web 2.0 Social networking explosion, this seems to have a very definate set of design rules and a lot of people are updating sites to take these into account to try and appear to be fresh and 'trendy'