I'm being asked by the company I work for to extend my notice period. I'm not outright against it (in fact it's somewhat flattering in a way) but it has made me wonder what a typical notice period might be for a C# software developer?
2 weeks is bare-minimum in the US (you may want your question to be less localized and made relative to what is considered standard) for most jobs. I'm relocating, but want to work remotely for my current company. They've asked for 3 months notice if I leave within the next 9 months. I couldn't sign that fast enough. There are no penalties stipulated.
As an employer I see it differently. If the employee is integral to the core product, no matter their job title, and if it is difficult to recruit replacements (perhaps due to location) and if the company feels there has been a historical lack or insufficient documentation then 3 months would be standard and appropriate length of notice.
It protects the employee to give time to find another job if the company gets into difficulties and it protects the company to give it confidence to offer good development programmes and investment is staff and working environment.
It should be remembered employment should be a two way relationship. And many many more people leave their employ by their own decision than the companies decision.
The company has to think of what is left after you leave and the protection of all the other employees you leave behind. It's not a service.
In the UK you'll sometimes see something like 2 weeks, plus 1 week per year worked over 2 years, up to 12 weeks. So the longer you've worked there, the longer the notice period.
As pointed out by Mumbles in the comments below, this is the legal default as given on Directgov.
However, 1 month is fairly typical, as others have stated.
One month is the typical notice period. Note that it's also the period the next employer expects you to join after. So, if you agreed to extend your notice period to be more than the typical in the market in your country, it may cause you a problem if you decided to move. Either you will be rejected because you will take too long to join or you will have to make a deal of some kind with the original employer to be able to leave.
My advice is to stick to the typical.