Maintenance Frequency at a Glance is a free tools which makes clear what the relation is between the maintenance frequency and the number of broken links at your site.
Maintenance Frequency at a Glance is based on research regarding link rot in a copy of the old Yahoo! directory.
Based on the acceptable percentage of broken links the tool calculates the frequency at which you should check broken links (and repair them of course).
At the other hand the tool gives you the expected percentage of broken links based on the frequency you want to check your website.