Preventive Maintenance Schedule

Overdue Services is based purely on mileage math: it checks whether Current Mileage has already passed the mileage due for each service (last service mileage plus that service's interval). Monthly Miles only comes into play when converting the remaining mileage into a projected number of months until each service, so a vehicle can show overdue services regardless of how many or how few miles you drive per month.

Est. Annual Maintenance is a forward-looking projection built only from Monthly Miles and Vehicle Type -- it estimates how many oil changes, tire rotations, and other services a typical year of that driving pattern requires and prices them out. It deliberately ignores whether you're currently overdue or up to date, since being behind doesn't change how many services a normal year ahead will require.

Yes -- raising Current Mileage while holding the last-service mileages fixed can only move each service closer to (or past) its due mileage, never further away, so Overdue Services can only stay the same or increase as Current Mileage rises across this calculator's full range. It never decreases from a higher Current Mileage alone.

Vehicle Type selects a different set of mileage intervals and per-service cost estimates -- heavy-duty trucks get longer oil and tire intervals (10,000 miles) than sedans (7,500 miles) but higher per-service costs, while SUVs, pickups, and vans share a shorter, mid-cost schedule. Changing Vehicle Type therefore shifts both which services show as due soon and the Est. Annual Maintenance total, even with identical mileage inputs.