The standard rates for interpreting are conditional upon local market particularities but, in general, similar rates apply across all linguistic combinations and different subject-matters. Usually interpreters are engaged on a daily basis and an hourly charge is not an accepted practice. However, a slightly lower rate may be agreed upon if the service is required only for half a day or for a couple of hours.
An overriding factor in the rates for interpreting is the number of professionals working on the project. Interpreting is a team work. Interpreters work in pairs or, more rarely, even in teams of 3 should the conference/congress/event exceed the 8-hour schedule. They take turns every 20 or 30 minutes, as research has shown that interpreting (particularly simultaneous interpreting) is one of the most stressful professions. Interpreters cannot and should not work on their own for a long time as their performance will fall short in quality.