Preventive Maintenance Schedule Calculator
Calculate maintenance intervals, next service dates, and annual maintenance costs based on equipment usage patterns and service requirements.
Formulas Used
Next Service Date (Time-Based):
Next Service Date = Last Service Date + Time Interval (days)
Days Until Service (Usage-Based):
Usage Remaining = Usage Interval − Current Usage Since Last Service
Days Until Service = Usage Remaining ÷ Average Daily Usage
Combined Mode:
Next Service = MIN(Time-Based Date, Usage-Based Date)
Annual Services:
Time-Based: Annual Services = 365 ÷ Time Interval
Usage-Based: Annual Services = (Daily Usage × 365) ÷ Usage Interval
Combined: Annual Services = MAX(Time-Based Annual, Usage-Based Annual)
Annual Costs:
Annual Maintenance Cost = Annual Services × Cost Per Service
Annual Downtime Cost = Annual Services × Downtime Hours × Hourly Operating Value
Total Annual Cost = Annual Maintenance Cost + Annual Downtime Cost
Interval Progress:
Progress (%) = (Elapsed Days ÷ Time Interval) × 100 | or | (Current Usage ÷ Usage Interval) × 100
Assumptions & References
- Time-based intervals assume calendar days (not business days).
- Usage-based intervals assume consistent average daily usage throughout the year.
- Combined mode triggers service at whichever threshold (time or usage) is reached first, per ISO 55000 asset management standards.
- Annual downtime cost assumes the equipment generates value equal to the hourly operating rate during all downtime hours.
- Maintenance cost does not include parts or materials unless included in the per-session cost input.
- Overdue status is flagged when the current date exceeds the calculated next service date.
- Urgency thresholds: Overdue = past due; Critical = ≤7 days; Warning = ≤30 days; On Track = >30 days.
- References: ISO 55000 (Asset Management), SAE JA1011 (Reliability-Centered Maintenance criteria), SMRP Best Practice Metrics.