Its very hard you can as you know look at what you did last year. look at how the power cost have risen in your area add that in . increase it by 1-3% But there is always that unknown factor. I have to have a new line installed for internet. They will pay for some but not all due to how far they have to run the cable. It will be 300 on my end but thats just one of the little items.. A few bulbs in the shop need replacement and I have a several ballasts that are going bad. They are no longer made so buy new and re wire or opt for a higher cost no ballast led bulb.
Breakage is another factor .. I know add a shop fee to every bill. I started looking at cost of brake cleaner, solvent tank charges , blast media, shop towels loc tite, anti seize copper spray etc etc those are the small things that do not seem like much until the end of the year and you find that you lost a bunch of money.. Add being its not even a item that you can say charge a whole bottle to the customer its up to you to figure in how much is used on each job.
Then labor efficiency , how are the jobs really going are you completing them in the time frame for the bid or are you over often under etc.
Here is one example I dyno tune Cost of the dyno 38,000 dyno booth 43,000 electrician to wire it all in 3,200, Roofer and construction of air intakes and exhaust outlet 4,100 , Computers, monitors another 1,300. 89,6000 in one item. Shop rate is 90 per hour dyno rate is 100 ( cost of the power) time to tune is 4.5 hours . so I charge 450 for a tune.
However many of these do not have the correct plug wires on them , or spark plugs , I have to test fuel pressure, check CCP ( as many DIY guys install the cams wrong and they are out of time ) So thats is another .25 in labor time. Then I also need a 18 mm bung inthe pipe for my WB sensors , ok some pipes have them others do not. If they do not I have to remove heat sheilds install 3/8 riv nut into the head pipe. SO now you have the 11 cost on the riv nuts plus a total of .5 extra labor there .
I tune 150-200 bikes a year so lets use 175 lets take the extra labor split it in half .375 65.62 hours X shop rate $5906 in a year was given away . That is where the little things bite . It does not seem like much at the time but end of the year it a dumb mistake . That is where you need to make some changes on how you do things