Example data table
| Scenario | Period | Output | Labor | Energy | Maintenance | Overhead | Contingency | Total OPEX |
|---|---|---|---|---|---|---|---|---|
| Baseline small plant | Monthly | 1,000 units | $15,000 | $2,360 | $2,300 | 8% | 5% | $26,320 |
| Higher utilization | Monthly | 1,300 units | $15,000 | $2,650 | $2,450 | 8% | 5% | $27,890 |
| Maintenance-heavy | Monthly | 1,000 units | $15,000 | $2,360 | $4,200 | 8% | 5% | $28,315 |
Formula used
- Energy Cost = (kWh × rate) + fixed fees
- Consumables Cost = fixed + (per-unit × output)
- Base Cost = sum of all entered cost categories
- Overhead = Base × overhead% (or a fixed overhead amount)
- Tax = (Base + Overhead) × tax% (optional)
- Contingency = (Base + Overhead + Tax) × contingency%
- Total OPEX = Base + Overhead + Tax + Contingency
- Cost per Unit = Total OPEX ÷ output
- Effective Output = output × utilization%
How to use this calculator
- Select the period you want to budget (monthly, annual, or custom days).
- Enter operating days and expected output for that same period.
- Fill in labor, energy, maintenance, and facility costs.
- Choose overhead as a percent or a fixed amount.
- Optionally enable depreciation or indirect tax for your model.
- Set contingency to reflect operational risk and uncertainty.
- Click calculate to see totals, unit costs, and breakdowns.
- Download CSV or PDF to share with stakeholders.
OPEX Scope
Operating expense captures recurring cost to keep an engineered system running for the chosen period. This calculator groups labor, energy, maintenance, consumables, utilities, waste, facility charges, insurance, IT, and other site costs. For monthly planning, align inputs to accounting cutoffs and use operating days to reflect the production calendar. When comparing scenarios, keep output quantity consistent, then vary one driver to isolate impact on total OPEX and unit economics.
Energy Model
Energy is often a top driver because it scales with throughput and equipment loading. Enter metered kWh and a blended rate, then add fixed fees for demand charges and service components. If you only know a monthly bill, place that value in utilities and set kWh to zero. Track energy share as a percent of total OPEX; when it exceeds 25%, validate motor efficiency, compressed-air leakage, idle running, and peak-shaving controls.
Labor and Maintenance
Split labor into direct and contract lines to separate staffed shifts from call-out work. For maintenance, include planned services and corrective work orders; spares capture parts that do not sit in consumables. A reliability check is to compare maintenance plus spares against history; large swings may indicate deferred work or major shutdowns. Use utilization to create an “effective output” view, so partial loading reveals hidden cost per effective unit.
Overhead Controls
Overhead can be modeled as a percent of base cost or as a fixed allocation. Percent overhead works for early estimates, while fixed overhead suits mature sites with stable shared services. If indirect tax applies to your subtotal, toggle it on and enter the rate that matches your jurisdiction and exemption status. Contingency is applied last; typical engineering budgets use 3–10% depending on data quality, supplier volatility, and operational risk.
Unit Economics
Cost per unit converts total OPEX into a comparable metric across lines, products, or sites. Pair it with cost per operating day to evaluate staffing and scheduling decisions. If cost per unit rises while total OPEX is flat, output is dropping; investigate downtime, yield loss, or constraint shifts. Benchmark with internal baselines, then review the breakdown table to target the highest-share categories first. It supports vendor quotes and contract reviews.
FAQs
1) What should be counted as operating expense in this tool?
Include recurring costs: labor, power, maintenance, consumables, utilities, waste, rent, insurance, IT, and other site costs for the same period. Optionally add depreciation and indirect tax when your reporting model requires them.
2) How do I model a shutdown or partial-production period?
Use the same period for all inputs, then set operating days and output to match the shutdown month. Keep fixed items like rent and insurance unchanged, and adjust variable items like energy, consumables, and contract labor.
3) Why does utilization affect the utilization-adjusted cost per unit?
Utilization scales effective output, not the expense lines. When utilization drops, the same total OPEX is spread across fewer effective units, revealing the hidden cost of downtime, changeovers, and underloaded equipment.
4) When should I use percent overhead versus fixed overhead?
Use percent overhead for early estimates when allocations are uncertain. Use fixed overhead when you have stable shared-service budgets or chargeback amounts, especially for mature sites with consistent administrative structures.
5) How can I sanity-check energy and rate inputs?
Compare kWh per unit against historical meter data, and confirm the rate includes supply plus delivery. If you only know a bill total, enter it as utilities and leave kWh at zero to avoid double counting.
6) How do the download options work?
CSV exports the last calculated inputs, results, and breakdown saved on the server session. PDF is generated from the on-page results and breakdown table, so run a calculation first, then click Download PDF.