I found this spreadsheet a while ago and don't know the exact origin. I think the original goes back to a user named "HARRY" at cog-online.org but the spreadsheet attached here has been modified quite a lot from his original one. I can't take credit for the fancy calculations this spreadsheet does, but it works well if you are faithful in inputing your data.
Step 1: follow the link to the Google Sheets document
Step 2: click on FILE and MAKE A COPY
Step 3: follow the instructions on the spreadsheet to initialize it for your bike's mileage
You will need Google Sheets to use this spreadsheet. You might be able to copy it over to Excel, but not sure some of the formulas would work properly there.Link here