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Every purchase has two price tags.
This page reads the second one.

The first price tag is on the shelf. The second is what the thing costs to run for the rest of its life — and for anything that runs daily, the second tag is often the larger of the two. Three small calculators below, using the same arithmetic as Chapter 6 of the guide. The maths works in any currency.

Show results in: A symbol, not a conversion — enter all amounts in one currency and the results come back in it.

① Will this measure pay for itself?

For any upgrade — insulation, a rain barrel, a showerhead, sealing — divide what it costs by what it saves each year. The guide's rule of thumb: under 5 years is almost certainly financially sound over the measure's lifetime, because after payback the savings keep coming for years.

Measure payback

Example starting points from the guide — tap one, then replace with your own quote and bill:

Total cost of the measure materials + any installation, from your actual quote Saving per year on your bills compare two bills, or use the % savings in the guide's chapter tables against your annual spend Expected lifetime of the measure (years) optional — insulation 30+, LED 15, heat pump 12–15

② Which appliance is cheaper to own?

The energy label — ENERGY STAR, the EU A-to-G letter, India's BEE stars, the Energy Rating Label — is the second price tag printed on the box. Stars and letters are shortcuts; the number that matters is the same everywhere: kilowatt-hours per year. Find it on both labels and let the arithmetic decide.

Two appliances, total cost of ownership

Prefilled with the guide's fridge example — replace every number with the two machines in front of you:

Appliance A — shelf price Appliance A — kWh per year from the energy label

Appliance B — shelf price Appliance B — kWh per year

Your electricity price per kWh from your latest bill: total amount ÷ total kWh Years you expect it to serve fridge 10–15, washing machine 8–12, AC 10–15

③ Is the solar quote honest?

Before any salesperson holds your attention, hold a first-pass number: system size (kW) × your region's specific yield (kWh per kW per year). Specific yield runs from roughly 1,000 in cloudy high-latitude regions to 1,800+ in desert sun — the free Global Solar Atlas gives the figure for your exact location. If an installer's promise runs far above this arithmetic, ask them to show their working. And remember the guide's order of operations: seal, insulate, and shade first — every kilowatt-hour you stop needing is panel you don't have to buy.

Solar payback, first pass

System size (kW) from the quote — a typical home system is 3–6 kW Specific yield for your location (kWh/kW/year) look it up on the Global Solar Atlas, or use a band above Total installed cost from the quote Your electricity price per kWh uses the value from tool ② if you leave this blank

Where this sits in the guide

Tier 1 · under $100

LED bulbs, air sealing, aerators, pipe insulation. Payback 6 months to 2 years, in every climate. Start here.

Tier 2 · $100–500

Thermostat, rain barrel, ceiling fans or insulation top-up depending on your zone. Payback 2–6 years.

Tier 3 · $500+

Heat pumps, solar PV, deep retrofit — usually financed. Payback 5–15 years. Do the cheap tiers first: a tightened home needs a smaller, cheaper machine.

Chapter 6 of the guide carries the full financial ladder, the installer question lists for heat pumps and solar, and the appliance label systems by country. Read the guide (free PDF).