Climate Action ROI Calculator
Cost-benefit of climate mitigation actions.
About this calculator
This calculator runs a standard discounted-cash-flow analysis on a climate investment, treating avoided emissions as a dollar-valued benefit alongside direct energy savings. Each year's benefit — annual energy savings plus CO2 reduction tonnes times the carbon price you set — gets discounted back to present value at your chosen discount rate and summed over the project's lifespan, then compared against the upfront investment cost to produce net present value and a benefit-cost ratio (values above 1.0 signal a positive return). Internal rate of return is solved numerically with Newton's method, iterating until the discounted cash flows net to zero, so it reflects the same underlying benefits as the NPV figure rather than a separate estimate.
Simple payback period, by contrast, ignores discounting entirely and just divides investment cost by annual benefit — a useful gut check, but it can understate how long money is really tied up compared to the discounted view. The abatement cost output nets out energy savings before dividing by total CO2 avoided, so a genuinely cost-effective project like an efficient retrofit can show a negative dollar-per-tonne figure, meaning it pays for itself before any carbon value is even counted. The default carbon price of $51/tonne and the 3% discount rate both come from the federal Interagency Working Group's February 2021 interim social-cost-of-carbon guidance (a reinstatement of the Obama-era central estimate, adjusted for inflation); EPA's own subsequent 2023 update revised the central estimate substantially upward to roughly $190/tonne, so it's worth swapping in whatever price matches your jurisdiction's current guidance or the market price of the carbon credits you're actually transacting.
Inputs
Results
Net present value ($)
$11,647.00
≈ 8 months of rent
Figures current as of 2021. Source: Interagency Working Group on Social Cost of Greenhouse Gases, United States Government. Technical Support Document: Social Cost of Carbon, Methane, and Nitrous Oxide — Interim Estimates under Executive Order 13990. February 2021.
How to Use This Calculator
- Enter investment cost ($) and estimated annual CO₂ reduction (tonnes/yr).
- Set annual energy savings ($/yr), project lifespan (years), discount rate (%), and carbon price ($/tonne).
- Review Net Present Value, Benefit-Cost Ratio, Simple Payback (years), and IRR (%).
- A benefit-cost ratio above 1.0 means the climate investment pays for itself in present value terms.
How the result changes with Energy savings ($/yr)
| Energy savings ($/yr) | Net present value ($) |
|---|---|
| 600 | $2,720.00 |
| 900 | $7,183.00 |
| 1,800 | $20,573.00 |
| 3,000 | $38,426.00 |
What each input means
- Investment cost ($)
- Upfront cost of the climate action or efficiency project.
- CO2 reduction (tonnes/yr)
- Estimated annual CO2 reduction in metric tonnes.
- Energy savings ($/yr)
- Annual dollar savings from reduced energy consumption.
- Project lifespan (years)
- Expected useful life of the project in years.
- Discount rate (%)
- Annual discount rate for NPV calculations. EPA uses ~3%.
- Carbon price ($/tonne)
- Social cost of carbon or market carbon credit price per tonne CO2.
What each result means
- Net present value ($)
- NPV of all benefits minus investment cost.
- Benefit-cost ratio
- Ratio of discounted benefits to investment cost. >1 means positive ROI.
- Simple payback (years)
- Years to recover investment from annual savings.
- Internal rate of return (%)
- Annualized rate of return on the climate investment.
- Annual benefit ($)
- Combined annual energy savings and carbon value.
- Total CO2 avoided (tonnes)
- Cumulative CO2 reduction over the project lifespan.
- Abatement cost ($/tonne)
- Net cost per tonne of CO2 avoided after energy savings. Negative means net savings.
- NPV of benefits ($)
- Present value of all future benefits discounted to today.
How this is calculated
Worked example, using the default values
- Identify Input Parameters4 parametersInvestment cost ($) = 10000, CO2 reduction (tonnes/yr) = 5, Energy savings ($/yr) = 1200, Project lifespan (years) = 20 = 6 input(s) provided
- Calculate Net present valueNet present value = npvBenefits - investmentCost11647 = $11,647
- Calculate Benefit-cost ratioBenefit-cost ratio = npvBenefits / max(1, investmentCost)2.16 = 2.16
- Calculate Simple paybackSimple payback = Math6.9 = 6.9
Figures and sources
- Default carbon price ($51/tonne) and 3% discount rate (2021) — Interagency Working Group on Social Cost of Greenhouse Gases, United States Government. Technical Support Document: Social Cost of Carbon, Methane, and Nitrous Oxide — Interim Estimates under Executive Order 13990. February 2021.
Engine last updated . Checked against 2 independently-derived tests — how we verify calculators. Built by Paul Gunder, a software engineer, not a licensed financial, medical, or legal professional.
Frequently Asked Questions
Why can the abatement cost per tonne come out negative?
The calculator subtracts total energy savings (annual energy savings times project lifespan) from investment cost before dividing by total CO2 avoided. If the project's lifetime energy savings exceed its upfront cost, that numerator goes negative, meaning the project pays for itself on energy savings alone even before you count a dollar of carbon value — an efficient retrofit is a common example.
How does this calculator's IRR differ from the benefit-cost ratio?
Benefit-cost ratio compares NPV of benefits to investment cost at your chosen discount rate — it tells you whether the project clears that specific hurdle rate. IRR instead solves numerically (via Newton's method) for the discount rate at which NPV would equal exactly zero, so it's the project's own break-even rate of return, independent of whatever discount rate you entered elsewhere.
Why does simple payback period disagree with the discounted numbers?
Simple payback just divides investment cost by annual benefit with no discounting at all, so it always looks more favorable than the NPV-based view once you're past the first year or two. It's included as a quick gut-check, but for any project with a discount rate above zero, it will understate how long your money is genuinely tied up before it's recovered in present-value terms.
Where does the $51/tonne default carbon price come from?
It's the federal Interagency Working Group's February 2021 interim social cost of carbon estimate at a 3% discount rate — a reinstatement of the Obama-era central value, adjusted for inflation, that the Biden administration used as a placeholder while a fuller methodology update was underway. EPA's own November 2023 update revised its central estimate up to roughly $190/tonne, so the $51 default here is intentionally conservative; enter your own jurisdiction's current guidance or an actual carbon-credit market price if you have one.
What happens if I set the carbon price to $0?
Annual benefit collapses to just the energy savings term, since the CO2-reduction-times-price component drops out entirely. NPV, benefit-cost ratio, and IRR then reflect a pure energy-efficiency investment with no carbon value attached, which is useful for seeing whether a project stands on its own merits before any credit for emissions avoided.
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