Is there a way to find out the percentage of how off my motorcycles odometer will be with non-stock gearing?

The front and rear sprockets on my
Honda CBR600 have 15 teeth in front and 45 teeth in the back. Stock gearing for my bike is 16 teeth front and 43 teeth back. I was wondering is there a formula or anyway I can figure out roughly the percentage my speedometer and odometer is off by?

Actually, the speedometer is driven from the motorcycle's FRONT wheel, so a change in sprocket gearing to the rear wheel won't make a difference.

One ratio is 1:3 and the other is 1 :2.5
It will be out a bit but you may be able to correct that with a different profile measurement on the tire

Most bike speedos are pretty optimistic. Best bet is t ofind a 1 mile stretch of road (or 1 km) between mileposts. & traverse it at 60 miles/hr (60 km/hr) keeping bike speed steady. & record how long it takes you with a stop watch. Should be exactly 60 seconds.
Actual speed is 60 x 60/actual seconds

Like dude the toe bone's connected to the foot bone, and the odometer's connected to the speedometer. Ride your bike a calibrated mile, or a mile checked with a GPS, and look at your odometer. The number of tenths of a mile it's off is the percentage it's off. One tenth off is ten percent (10%). If you ride a measured 100 miles each mile off will be one percent (1%).

Your bike has one-tooth smaller sprocket on the gearbox output shaft, and two-teeth bigger sprocket on the back wheel. So it has been geared down quite severely. The previous owner was probably after more instant response (or liked doing monos) around town at the expense of busier motor and increased fuel consumption on the open road.
Your final drive ratio is 45/15 or exactly 3 to 1
The OEM 43/16 drive ratio is 2.675 to 1
In other words it takes three rotations of the front sprocket to turn your back wheel one full revolution, instead of the OEM 2.675 times. Put another way, at any given road speed (rear wheel rpm) your drive sprocket (and therefore engine) rpm is higher than the OEM bike by approximately 12%, because your rear wheel has to turn a certain number of times to cover a fixed distance. On your bike 100mph actual will be indicated as 112mph, and every 1,000 miles covered will be recorded as 1,120miles. This is if your speedo/odo are driven off a gearbox sprocket sensor. If the speedometer drive is in the front wheel hub, then none of this matters. Note that speedometers are usually always optimistic. You can use a Sat Nav/GPS to check the speedo accuracy; though not precise, they are accurate enough for the purpose.

Use a gps or a speedo app on your phone. My NC700 needs to show 107 on the speedo to be doing 100. I checked with two devices.

The speedometer and odometer on a CBR600 will be unaffected by gearing changes. The only thing different will be the engine rpm at a particular road speed, with stock final drive gearing your engine would spin almost 11% slower in every gear for any given speed.

Use a portable GPS to compare actual motion to speedometer reading.

The speedo is taken off the front wheel, (On Your 'sickle), not the back. No change, she isn't a car.

EDIT: ID Care whom out there has it taken off the back wheel or gearbox; question was about Kyle's CBR600

EDIT: Only if taken off gearbox Could a sprocket change affect it. Even If driven off R wheel (it Isn't in your case), only tire changes from stock height affect it. Same with F drive.

I'll bet Few out there have speedo to anything But front wheel. Look, Don't just Argue w/JD for Sake of argument. The cable rotates, so it Must be kept short. Only possibly an electric speedo may have a Hall effect sensor and a wire anywhere but F wheel. Even my short F cable and drive gear went after only 20k. A 6' long cable will Knot itself, without clamps everywhere.

Since most 'bikes have speedo on head race, the cable would have to flex as well if anywhere but going to F wheel. Going to F wheel negates any need to flex on steering.

If the wheel is still the same size as when you got the bike then nothing changes. Your speedo is measured by the rotations of the front wheel. A smaller wheel means it rotates faster and more per mile so the odometer is out. If the wheel is oversized then less rotations per mile so the readings are out again. You normally never change that wheel.
. If you make the rear sprocket larger then you would be able to do wheelies easier but have a lower top speed. You would also have to make the chain longer by a couple of links.
. The reverse is true if the sprocket is smaller. It does not affect the odometer accuracy at all.