Most Indian SME owners know their machines break down. Fewer know what each hour costs. A bottleneck machine producing ₹500/hour in margin sits idle for 8 hours because a bearing failed — that is ₹4,000 gone before you call the mechanic. Yet the same owner hesitates to spend ₹15,000 on preventive maintenance, because the benefit is invisible on paper.
This article builds the downtime ledger — the one document that converts lost production into a number, so you stop treating maintenance as expense and start treating it as insurance with a measurable claim value.
Advisory
Most owners know monthly revenue, few know gross margin per machine-hour. Take a bottleneck machine: if it runs 16 hours/day, 25 days/month, and contributes ₹8 lakhs/month in gross margin (revenue minus material and direct labour), that is ₹200/hour. An unplanned 40-hour breakdown — common for a worn spindle bearing — costs ₹8,000 in lost margin alone, before idle labour, missed customer deadlines or penalty clauses. Calculate margin/hour for each machine by dividing monthly gross margin (by product or product family) by actual running hours; separate planned maintenance windows (count as zero hours at risk). This becomes your Damage Per Hour. Once it is visible, every maintenance decision earns a payback threshold.
Downtime carries two hidden costs beyond lost margin. First, fixed costs (rent, salaried salaries, insurance, depreciation, utilities baseline) keep running: a machine idle for 8 hours still costs you 33% of that day's fixed overhead. If your plant's monthly fixed cost is ₹10 lakhs across, say, 4,000 running machine-hours, each idle hour absorbs ₹25 in fixed cost. Second, restart cost: re-setup time, scrap during ramp-up, quality checks, and the labour hours to clear a queue accumulate. In practice, a 6-hour unplanned stop often wastes 10 hours of calendar time. Maintain a weekly Downtime Register (Excel or printed sheet at the plant head's desk): record machine, stop time, cause (bearing, hydraulic, electrical, tooling, material shortage, operator error), duration, restart waste, and restart date. At month-end, sum the register by cause, multiply hours by your calculated ₹/hour (margin + fixed-cost + restart), and match against maintenance spend. A bearing replacement that takes 2 hours, costs ₹3,000 and prevents one 40-hour unplanned failure pays back in under two months.
Preventive maintenance (PM) is scheduled downtime at planned cost; failure is unscheduled downtime at much higher cost. A 4-hour bearing inspection and oil seal replacement (₹5,000, ₹2,000 labour, ₹3,000 parts) might be scheduled for the first Saturday of each quarter. If it prevents one 40-hour catastrophic failure (₹8,000 margin loss + ₹200 fixed cost + ₹1,000 restart waste), the PM pays 187% ROI annually. Start by calculating your actual failure cost for the top three failure modes (use your Downtime Register from the last 12 months). Then cost out a preventive regime for each. The ROI is: [(Failure Cost × Prevention Rate) − PM Cost] / PM Cost × 100. If your bearing failures occur once every 18 months at ₹9,000 total cost, and quarterly PM at ₹5,000 cuts failure risk to one every 4 years, your annual PM spend is
Frequently asked questions
Calculate gross margin per machine-hour by dividing monthly gross margin by actual running hours. Multiply this by downtime duration in hours, then add fixed cost absorption (monthly fixed costs ÷ total running hours × idle hours) to get total downtime cost.
Downtime costing includes lost gross margin, fixed cost absorption (rent, salaries, utilities continuing during idle time), and restart costs such as re-setup time and scrap during ramp-up.
By quantifying the hourly cost of breakdowns, you can compare it against preventive maintenance costs—for example, ₹4,000 lost margin from an 8-hour breakdown justifies ₹15,000 preventive maintenance that prevents recurring failures.