Gather inputs before trusting an ROI result
Collect current waste contractor invoices and weighbridge/collection records, not assumed daily savings. Then gather the machine quotation including GST, freight and commissioning; metered kWh or defensible operating estimates; labour, spares, additives, annual maintenance, and curing costs.
- Record actual daily source-segregated wet waste (kg), and operating days/year.
- Use documented electricity and labour expenses attributable to this activity.
- Include sorting, rejects, curing and lawful final disposal.
Cost per kg and annual net benefit: formulas
The basic comparison is annualised operating spend divided by kg of incoming segregated organic waste processed. Indicative simple payback uses initial installed capital divided by annual net cash benefit. If net benefit is zero or negative, simple payback is not achieved under those assumptions.
| Metric | Calculation | Common omission |
|---|---|---|
| Annual input (kg) | kg/day × operating days | Peak/holiday load, rejected waste |
| Annual operating cost | Power + labour + AMC + consumables + curing + other | Operator, moisture correction and transport |
| Cost per kg | Annual operating cost ÷ annual kg input | Different input vs output weight |
| Annual net cash benefit | Verifiable avoided spend − total annual running spend | Invented carbon credits/compost sales |
| Simple payback | Installed capex ÷ positive annual net benefit | Finance, taxes and replacement capex |
Use a sensitivity range, not one confident figure
Change power units, staff time, annual days and expected spare replacement expenses. Also calculate 50%, 75% and 100% utilisation cases. A machine purchased for 200 kg/day but loaded with only 70 kg/day can show a much higher cost per kg.
- Do not count avoided disposal charges unless the current contractor actually bills by that waste stream.
- Do not assume raw machine discharge is instantly saleable mature compost.
- Add permit, site upgrade and finance costs for a full investment appraisal.
When this calculator is useful
Use the editable estimator as a preliminary procurement screening tool. After shortlisting, request a vendor-specific load schedule and a site visit. The final business case may include non-cash compliance or housekeeping benefits, but they should be presented separately from financial savings.
The estimator excludes financing, depreciation, taxes, inflation and the time value of money.
Request a comparison-ready written quotation
Ask every vendor for connected load, expected duty cycle assumptions, standard accessories, warranty, commissioning, consumables, annual service coverage, expected spare classes and post-processing requirements. Quotation scope—not just capacity—drives the economic model.
When the question becomes model-specific
This guide stays general. For exact figures on a particular machine, these published pages from the COMPOSTO range are the reference.
Want a second opinion on your site?
Send your site type, city and measured daily wet waste. The COMPOSTO technical team replies with the capacity and checks worth doing next.