A very difficult question to answer as there are so many variables. The biggest and most important variable is how much use the appliance gets. If a fire is lit twenty four hours a day, seven days a week then it is going to need a lot more sweeping than a fire used occasionally in the evening.
Other variables include the type of appliance, fuel used, moisture content of the wood, type of chimney (how straight or smooth), location of flue (whether within the building or new system installed up the outside of the house), height of chimney, downdraughts. Every chimney is different and behaves differently.
If in any doubt then get the chimney swept now and I can advise the future frequency of sweeping.
After sweeping every chimney I issue a NACS certificate of sweeping and this will include when the next sweep is due.