How long do isp keep browsing history and what information do they delete after the retention period?
What happens when ISPs delete logs and police approach them asking to resolve an IP address at a particular time on a particular day to a real person and their details (contact, address etc..)? Does "deleting logs" mean deleting the record of which subscriber was assigned what dynamic IP address and when? Or ISPs never delete data about who had what IP and when, but just delete what they had accessed and for how long?
In a nutshell, explaining how long do isp keep browsing history leads to understanding that the duration and scope of data retention is dictated by legal requirements, and then operational/business decisions may come into play. ISPs may or may not be allowed to keep logs for longer than legally necessary but storage and maintenance has a cost. Unless there is value in mining that particular data, the incentive for an ISP to keep logs forever is low.
The most important (and possibly the only) information that the ISP can provide is whose connection was assigned what IP address at a given time. The aim being to identify a customer from an IP address recorded somewhere else (eg in web servers logs). The ISP probably doesn't have so much insight into your browsing activity. If you use their DNS they may figure out what websites you visited, but many people use a third-party DNS like Google, Quad9 etc. Even if the ISP tapped your whole traffic because you are a "person of interest" most of it would be encrypted anyway (https mostly). If the police need more details about what you did on some website where your IP address was recorded, then the police would have to subpoena the webhost or whatever. The ISP has only part of the information, which is crucial for investigations but very limited at the same time. Read the terms and conditions of your ISP and see if there is any mention of what data is logged.