Greenhouse vs Store Produce Cost Calculator

Building a backyard greenhouse can deliver year‑round vegetables, better seedling protection, and more control over pests and weather. It can also be a meaningful investment: materials, glazing, ventilation, heating, irrigation, and periodic repairs all add up. This calculator estimates whether a greenhouse “pays for itself” financially by comparing:

• What you would spend buying the same amount of produce from a store, versus
• What you spend producing it in the greenhouse (upfront setup + ongoing annual costs).

The result is a break‑even (payback) time and a cumulative savings estimate over your chosen analysis period.

Inputs (what each number means)

• Greenhouse setup cost (G): One‑time cost to build/buy and get the greenhouse operational (structure, glazing, benches, fans, irrigation components, etc.).
• Annual operating cost (O): Yearly out‑of‑pocket costs to run it (electricity/heat, water, soil/amendments, fertilizer, seeds/starts, replacement plastic, pest control, small repairs).
• Annual produce yield (Y): How much edible produce you expect to harvest each year, in kilograms.
• Store price per kg (S): The price you would otherwise pay per kilogram for comparable produce (average your receipts over time for realism).
• Years of analysis (N): How many years you want to model cumulative totals for.

Formulas used

Annual store spending for the same quantity of produce is:

Store cost per year = S × Y

Annual net savings from the greenhouse (compared to buying) is:

Annual savings = (S × Y) − O

If annual savings is positive, the break‑even time (payback period) is:

If (S × Y − O) ≤ 0, then there is no payback under these assumptions because the greenhouse does not reduce annual spending versus buying (operating costs are too high and/or yield/store prices are too low).

Interpreting the results

• Payback time (t): The estimated number of years for cumulative savings to equal the upfront setup cost. A payback of 3–5 years is generally “fast”; 10+ years may be reasonable only if you expect to keep the greenhouse and use it consistently for a long time.
• Cumulative savings after N years: An estimate of total difference after your selected horizon:
  • Greenhouse net = −G + N × ((S × Y) − O)
  • Positive means the greenhouse is ahead financially by that amount; negative means buying is still cheaper by that amount.
• “No payback” case: This doesn’t mean a greenhouse is a bad idea—only that the financial savings on groceries alone don’t cover the costs in your scenario. Many owners still value season extension, quality, variety, and enjoyment.

Worked example

Suppose you spend $2,500 to build a modest greenhouse, with annual operating expenses of $300. You harvest about 250 kg per year, and comparable produce costs about $4/kg at the store.

• Store cost per year = 4 × 250 = $1,000
• Annual savings = 1,000 − 300 = $700
• Payback time = 2,500 / 700 ≈ 3.6 years

Over a 10‑year horizon, cumulative net savings would be:

−2,500 + 10 × 700 = $4,500

Scenario comparison (example numbers)

Note: This table uses the worked example inputs (G=$2,500, O=$300/year, Y=250 kg/year, S=$4/kg). Your results will differ.

Assumptions & limitations

• Labor is not included: Your time (planting, watering, pruning, harvesting) is not monetized. If you want to include it, add an estimated annual labor value into operating cost (O).
• Financing and opportunity costs are excluded: Interest on loans, lost investment returns, and cash‑flow timing are not modeled.
• Repairs and replacements are simplified: Major repairs (heater replacement, glazing failure, storm damage) can make costs lumpy rather than “annual.” You can approximate by increasing O or adding expected repair costs averaged per year.
• Yield varies: Climate, crop mix, skill, pests/disease, and seasonal heating constraints can change Y substantially year to year.
• Quality and variety differences: Homegrown produce may be higher quality or different varieties than store produce; the “equivalent store price” S is an approximation.
• Taxes, depreciation, and resale value are not included: Some setups may add property value or have salvage value; others may not.

Tips for choosing realistic inputs

• Estimate yield (Y) using garden logs, past harvest weights, or conservative projections by crop type; if unsure, start low and run a sensitivity check.
• Estimate store price (S) as an average over several weeks/months (seasonal spikes matter).
• Operating cost (O) is often driven by heating and electricity. If you heat in winter, include a realistic portion of your energy bills.