The difference between carbon offsets, credits, and allowances

Why these terms are frequently confused

The terms carbon offset, carbon credit, and carbon allowance are often used interchangeably in media coverage and corporate sustainability reports, but they describe structurally different instruments. According to the World Bank’s State and Trends of Carbon Pricing 2023 report, more than 70 carbon pricing instruments are now in operation globally — spanning voluntary offset markets, regulated credit schemes, and mandatory cap-and-trade systems. Each category functions under different rules. Conflating them leads to misreading corporate climate claims, overestimating the stringency of a given policy, or purchasing the wrong instrument for a stated goal.

Carbon pricing, broadly defined, is the mechanism by which governments and regulators embed the external cost of greenhouse gas emissions into the price of economic activity. The Intergovernmental Panel on Climate Change (IPCC) Sixth Assessment Report (2022) identifies carbon pricing as one of the most cost-effective policy instruments for achieving large-scale emissions reductions. The three instruments below represent the main approaches through which that pricing operates.

Carbon offsets: project-based certificates for the voluntary market

A carbon offset is a certificate representing one metric ton of CO₂e that a specific project has reduced, avoided, or removed from the atmosphere. Offset projects include reforestation, avoided deforestation (REDD+), methane capture from landfills, and renewable energy installations in developing markets. An independent third party must verify each offset before the registry issues it as a tradeable certificate.

Offsets primarily operate in the voluntary carbon market — meaning participation is not legally mandated. Individuals and companies purchase offsets to compensate for emissions they have not yet reduced. Purchasing and retiring a credit removes it from circulation in a public registry permanently — it cannot be resold or double-counted. The two most widely used voluntary standards are the Verified Carbon Standard (Verra VCS) and the Gold Standard, both of which require independent auditing and public registry listings.

Carbon credits: tradeable units in baseline-and-credit systems

A carbon credit is a tradeable unit issued when an entity reduces its emissions below a defined baseline. In a baseline-and-credit system, regulators set an expected emissions level for each participant. A company that emits less than its baseline earns credits for the difference — credits it can sell to other companies that have exceeded their own baselines. The system creates a financial incentive to reduce emissions: companies that cut more than required generate an asset; companies that cut less must buy.

Carbon credits differ from offsets in one important structural way: credits are generated by regulated industrial actors reducing their own operational emissions, while offsets are generated by discrete projects (often in different sectors or geographies) that reduce or remove emissions on behalf of others. The Clean Development Mechanism (CDM), established under the Kyoto Protocol, operated as the largest baseline-and-credit system of its era — issuing Certified Emission Reductions (CERs) to projects in developing countries that industrialised nations could then purchase to meet treaty commitments.

Carbon allowances: permits inside a cap-and-trade system

A carbon allowance is a permit issued by a government or regulatory body that grants the holder the right to emit one metric ton of CO₂e. Allowances operate inside cap-and-trade systems, where the total quantity of permits in circulation is fixed — the cap — and that cap declines over time, mechanically tightening the emissions ceiling across the covered sector. The European Union Emissions Trading System (EU ETS), established in 2005, is the largest and most studied cap-and-trade system in operation, covering approximately 40% of EU greenhouse gas emissions across power generation, industry, and aviation, according to the European Commission.

Allowances are distributed in two ways: free allocation (given to certain industries at risk of carbon leakage) and auctioning (where companies purchase permits at market price). Companies must surrender allowances equal to their verified annual emissions. A company that emits more than it holds allowances for faces financial penalties. Surplus allowances — where a company emits less than its allocation — can be banked for future use or sold on the carbon market. This secondary market sets the price signal that determines the cost of emitting within the capped system.

How the three instruments compare

The table below summarises the key structural differences across the three instrument types.

What this means for individuals calculating their footprint

For individuals, the relevant instrument is the carbon offset — purchased voluntarily through the voluntary carbon market after measuring and reducing their personal footprint as far as practical. Carbon allowances and compliance credits operate at the industrial and governmental level; an individual cannot participate in the EU ETS or purchase CDM credits for personal use.

Offsets should be understood as a complement to emissions reduction, not a substitute. The GHG Protocol’s guidance on corporate accounting makes clear that purchased offsets do not reduce an entity’s reported Scope 1 or Scope 2 emissions — they are accounted for separately. The same logic applies at the individual level: a ton offset is not the same as a ton not emitted. Reduction first, offsetting second is the correct sequence. For more on how personal emissions are estimated and categorised, see Decarb’s methodology.

Flight emissions are a common trigger for offset purchasing. As detailed in Decarb’s analysis of US flight emissions, a cross-country round trip produces approximately 0.608 tons CO₂e — roughly one verified offset certificate. That certificate, once retired, cannot be resold.

Frequently asked questions

What is the difference between a carbon offset and a carbon credit?

A carbon offset is a certificate generated by a project that reduces or removes one ton CO₂e from the atmosphere — typically sold in the voluntary market to individuals or companies seeking to compensate for their own emissions. A carbon credit is a tradeable unit generated when a regulated industrial emitter reduces its emissions below a defined baseline; it operates inside a compliance system and can be used by other regulated entities to meet their obligations. The two instruments are generated by different actors, under different rules, for different buyers.

How does a cap-and-trade system work?

In a cap-and-trade system, a regulator sets an absolute ceiling — the cap — on total emissions within a covered sector, dividing it into individual allowances each permitting one ton of CO₂e. Regulators distribute allowances to regulated entities, either free of charge or by auction. At the end of each compliance period, every entity must surrender allowances equal to its verified emissions. Entities that emit less than their allocation can sell surplus allowances; those that emit more must purchase additional ones. The cap declines over time, mechanically reducing total permitted emissions across the system.

Can individuals buy carbon allowances from the EU ETS?

The EU ETS is a compliance market designed for regulated industrial and energy sector entities — power plants, manufacturers, and airlines operating within the EU. Individuals cannot directly participate as obligated parties. Some organisations have purchased and cancelled EU allowances voluntarily to tighten the cap, but this is not the standard mechanism for individual climate action. For personal footprint offsetting, the voluntary carbon market — using Verra VCS or Gold Standard certified offsets — is the appropriate channel.

Does buying a carbon offset actually reduce emissions?

A high-quality offset — independently verified, registered in a public registry, and retired on purchase — represents a real reduction or removal of one ton CO₂e that would not otherwise have occurred (the additionality requirement). Retiring that credit permanently removes it from circulation; no one can resell it. The emissions reduction is real, but it occurs elsewhere — not in the buyer’s own operations. This is why offsets are best understood as a compensation mechanism for residual emissions that cannot yet be eliminated, not a substitute for direct emissions reduction.

What does it mean when a company says it is carbon neutral?

A company claiming carbon neutrality is asserting that its net greenhouse gas emissions equal zero — typically by combining direct emissions reductions with the purchase and retirement of offset certificates. The claim is only meaningful if an independent auditor has verified the underlying emissions, the offsets meet recognised quality standards (such as Verra VCS or Gold Standard), and the accounting boundary is clearly defined. Decarb does not use the term “carbon neutral” for any entity unless those conditions are met. The term is frequently applied loosely, and scrutiny of the methodology behind any such claim is warranted.

Sources

1. World Bank, State and Trends of Carbon Pricing 2023. Washington DC: World Bank Group, 2023.
2. IPCC, Sixth Assessment Report, Working Group III: Mitigation of Climate Change. Cambridge: Cambridge University Press, 2022.
3. European Commission, EU Emissions Trading System (EU ETS). Brussels: European Commission, 2023. ec.europa.eu/clima/eu-action/eu-emissions-trading-system-eu-ets
4. Integrity Council for the Voluntary Carbon Market (ICVCM), Core Carbon Principles. ICVCM, 2023. icvcm.org
5. GHG Protocol, Corporate Accounting and Reporting Standard. Washington DC: World Resources Institute, 2004 (revised).
6. Verra, Verified Carbon Standard Program. verra.org/programs/verified-carbon-standard