How much time do researchers spend on writing grants? As a potential future researcher I would like to know how much I could focus on my research and how much distraction grants cause. My research interest lie in theoretical cs and logic, however the answers should include other areas so that they may be useful to other readers too.

Specifically, how many hours of your working day on average is dedicated to grant related issues - searching a grant, writing a grant proposal, writing the final report for the funded projects, etc.

I heard in an informal talk that this can be as much as half of the time of the researcher, say 5 hours, Monday to Friday. In such circumstance, I do not think I would be able to focus on the research.
It very much depends on the field, the researcher, and the grants. To give you a picture of someone who works in public health - in a soft money position - here's some things that occupy my time. I am however not faculty (I'm a postdoc) so if anything this is an underestimate.


Several weeks a year, almost everything else comes to a halt. Even when I'm not the PI on a grant, if I'm in charge of a section theres reading to do, figures to make, etc. Also often rigging up preliminary data etc., because working on mathematical models of infectious diseases means that for grant applications you have to outline the model itself - a substantial amount of work is already done.
I've spent probably a good month of productive working time managing a particular grant I have. This grant has been a problem child from day one - issues with the contract, issues paying things, issues, issues...it's depressingly not even for all that much money.
Usually then per-paper I spend about an hour making sure my acknowledgments point to the right grants, make sure things that should be in PubMed Central end up their, etc.