The calculator starts with a base service interval by asset type, then adjusts that interval using risk multipliers. Larger multipliers shorten the interval and increase visit frequency.
rawIntervalDays = baseIntervalDays ÷ (usage × environment × criticality × age × failures)
- Visits/year (per asset): ceil(365 ÷ finalIntervalDays)
- Total annual visits: visits/year × assetCount
- Annual cost (optional): totalVisits × effectiveCostPerVisit
- Pick the asset type that best matches your system.
- Enter asset count and operating schedule.
- Select the environment and criticality level.
- Provide asset age and failure history for realism.
- Add manufacturer or regulatory limits if applicable.
- Optionally enter cost per visit for annual budgeting.
- Press Calculate frequency to view the result above.
- Use the download buttons to export the report.
Sample entries showing how different conditions affect recommended frequency.
| Asset | Environment | Criticality | Usage | Age | Failures/Year | Recommended Interval (days) | Visits/Year |
|---|---|---|---|---|---|---|---|
| HVAC / Air Handling | Indoor (controlled) | Medium (standard) | 8h/day, 5d/week | 4 years | 0 | ~95 | 4 |
| Backup Generator | Outdoor (weather exposure) | High (production impacting) | 12h/day, 6d/week | 9 years | 1 | ~33 | 12 |
| Fire Alarm / Sprinkler | Coastal / salty air | Life-safety / code critical | 24h/day, 7d/week | 6 years | 0 | ~9 | 41 |
| Electrical Panels | Dusty / high particulate | High (production impacting) | 10h/day, 6d/week | 12 years | 2 | ~55 | 7 |
Service frequency as a risk control
Planned service visits reduce unplanned stoppages, safety incidents, and rework. This calculator converts site conditions into an interval that balances reliability and compliance. Start with an asset’s typical base interval, then tighten the schedule when risk drivers increase. Use the risk score to compare assets and justify preventive maintenance decisions. Document assumptions so supervisors and auditors can trace the logic.
Using operating intensity to adjust intervals
Operating hours and days per week act as a workload proxy. Higher duty cycles accelerate wear on bearings, belts, filters, seals, and electrical contacts. The model increases the usage factor for long shifts and seven‑day operations, shortening the interval in days. For intermittent assets, the factor decreases, preserving budget without under‑servicing. Pair the result with runtime meters when available.
Environment and criticality multipliers
Construction sites are rarely “clean rooms.” Dust, salt, moisture, and corrosive chemicals raise failure likelihood and inspection needs. Criticality captures business and life‑safety impact: life‑safety systems should be checked more frequently than non‑critical loads. When you enter manufacturer or regulatory maximum intervals, the final interval will not exceed those limits. Add notes for special hazards like welding fumes or silica.
Cost planning and crew loading
Frequency drives annual workload. The calculator converts the interval into visits per year per asset, then scales to total visits across all assets. If you add a cost per visit, you get an annual budget estimate. Use this output to size service contracts, forecast overtime, and coordinate access permits and shutdown windows. Track actual spend monthly and adjust unit costs for parts.
Turning intervals into a yearly schedule
A recommended interval is only useful when it becomes dates. The tool generates the next 12 visit dates from today, helping you align inspections with production peaks, weather constraints, and holiday closures. Review the schedule quarterly, update failure history, and re‑run the calculation after major site changes. Combine planned visits with inspections already required by permits to reduce disruption. Across teams.
What does the recommended interval represent?
It is the suggested maximum days between planned service visits for the selected asset type, after adjusting for workload, environment, criticality, age, and failure history. Shorter intervals mean more frequent visits.
How do manufacturer and regulatory limits affect results?
If you enter a manufacturer or regulatory maximum interval, the calculator will not recommend a longer interval than those limits. This ensures the plan stays within the strictest requirement while still reflecting site risk.
What if my site runs seasonal or changing shifts?
Update operating hours, days per week, and recent failures whenever the schedule changes. Recalculate at the start of each season or major phase. The new interval and dates will reflect the updated workload and conditions.
How should I estimate failures per year?
Use work orders or maintenance logs for the last 12 months. Count incidents that caused corrective repairs, downtime, or safety concerns. If data is limited, start conservative, then refine after you collect consistent records.
Can I calculate multiple asset types for one project?
Yes. Run the calculator once per asset type and keep separate exports. This helps you compare workload and costs across systems, then build a combined master schedule in your maintenance plan.
Why does higher criticality shorten the interval?
Critical assets have higher consequences when they fail, such as safety risk, code violations, or major downtime. Shorter intervals increase inspection and preventive work frequency, reducing the chance of severe failures and improving compliance confidence.