When the power goes out, the first question most owners ask is: “When will it come back?” The better question is: “How much does every hour without power cost me?” Because that number — not your nerves — is what tells you whether you need backup power and how much it makes sense to spend on it.

Many owners assume downtime just means a few missed sales. In reality the loss runs wider: stock spoils, wages get paid for hours when no one can work, and some customers simply go where the lights are on and never come back. Until you put a figure on it, that cost stays hidden — and it feels like something you can just “tough out.”

At LPF we’ve been helping small and mid-sized business owners since 2018 to count these things honestly, with no sugar-coating. Here’s how to estimate the cost of downtime yourself, on the back of a napkin, so you can talk about backup power in numbers rather than feelings.

What downtime actually costs

Before you calculate anything, it helps to see every part of the loss. Most people underestimate it because they only picture “the register that isn’t ringing.”

  • Lost revenue — the sales that simply didn’t happen while the lights were off. The most obvious part, but far from the only one.
  • Spoiled stock — anything that depends on refrigeration: food, prepared goods, medicine, flowers. A long outage can cost more than the missed sales themselves.
  • Paid idle staff — wages still accrue for the hours your people stand around unable to work.
  • Lost customers — someone who finds locked doors or a dead card terminal may go to your neighbour next time, permanently.
  • Broken commitments — missed orders, late shipments, promises to clients you couldn’t keep.

A simple formula you can do on a napkin

You don’t need spreadsheets. Just estimate the cost of a single hour of downtime and multiply it by the average number of “dark” hours per month.

  • Step 1. Revenue per hour — take your normal daily revenue and divide it by your working hours. That’s roughly what the business earns in one hour of trading.
  • Step 2. Keep the profit, not the whole revenue — apply your margin to that hourly figure. You don’t buy the stock you never sold, so count the real loss rather than turnover.
  • Step 3. Add your fixed costs — rent, wages and security run whether you’re open or dark. That money drains during an outage too.
  • Step 4. Multiply by hours without power — take the average monthly outage hours that fall within your working day. That’s your rough monthly cost of downtime.

This estimate is deliberately simple. The goal isn’t accounting precision down to the last coin — it’s a clear benchmark you can actually make decisions with.

The costs people forget

The basic formula captures the “trading” part of the loss. But there are costs owners often skip, and they can be significant.

  • Spoilage and write-offs — count separately the stock you have to throw out after a long outage.
  • Restarting equipment — some machines need time to come back up to temperature or working order after losing power.
  • Overtime and catch-up — when staff work extra hours to make up lost ground, someone pays for those hours too.
  • Reputation — a bad review or a customer’s habit of “not bothering with them anymore” has no price tag, yet it dents revenue for months.

Why bother counting at all

The point of the number isn’t to scare yourself — it’s to give your decision an honest anchor. Once you know the monthly loss, everything else becomes visible.

  • To compare with the cost of backup — knowing your monthly loss makes it easy to estimate how many months it would take for backup power or a reserve internet line to pay for itself.
  • To avoid overspending — you might only need a small “continuity island” for the register and lights, not a full station. The figure tells you the scale.
  • To decide calmly — a decision made with the math in hand is always measured, not bought on the wave of the latest blackout.

If you’re not confident in your own figures, we’re here to help. We’ll ask a few simple questions about your premises, help you honestly calculate the cost of downtime, and show you which backup makes sense for you and which would be wasted money. The design, the choice of solution and the monitoring are ours; the physical installation is handled by our trusted partner crew. Write to us — we’ll start with the math, not with selling you equipment.