How the estimate works
The next service is due at the last service reading plus the interval. Subtract the current meter to see how much is left. Divide that by your average use per working day and round up, and you have the number of working days to go.
Those working days are counted starting tomorrow. The working week starts on Monday and runs for the number of days you choose, so a five day week means Monday through Friday. Public holidays are not considered. The date is an estimate, not a promise.
If you also enter a calendar interval in months and the date of the last service, the calculator works out a calendar due date as well. Whichever comes first is flagged as due first. A service that is already past due shows in red.
Getting good readings
Set the service interval from the manufacturer’s manual, not a guess based on another machine. Check its guidance for severe duty and adjust the plan where the manufacturer calls for it. Dust, long shifts and demanding operating conditions can matter even when two machines share the same model badge.
A warning threshold gives the shop time to act before the due point. For example, a warning 25 hours before service leaves room to order parts, arrange shop time and talk to the operator. It is a planning warning, not an extension of the service interval. Choose a threshold that fits your actual daily use.
Use the meter reading on the day of the last service, not the reading from the work order. The current meter should be read today if you can. Average use per working day is the number most people guess, so try dividing the last month of meter hours or kilometres by the days the machine actually worked.
Pick hours for machines such as excavators and loaders, and kilometres for trucks. The mode changes the labels only. The arithmetic is the same.
The table lists the next five service points, each with its meter reading and estimated date. It helps you see when a service is likely to land in a busy season. The meter readings and calculated dates are not saved or sent. The form stays in this tab.
Beyond a one-off estimate
A calculator answers one machine at a time. When you have a whole fleet, the useful thing is a single view of what is coming due. Zerk keeps plans, readings and service history together, so the next service is visible without redoing the maths. Read more about preventive maintenance by engine hours and kilometres.
You can also use the equipment cost per hour calculator to see what the same machine costs to run.