Emissions Reduction Target Calculator
The annual reduction needed to take emissions from today’s level to a target percentage cut by a target year — as a constant yearly percentage and as a straight-line cut — with the emissions along the way.
A target such as “43% below today by 2030” can be met by cutting the same percentage every year (compound) or the same tonnage every year (linear).
How the emissions reduction target calculator works
A target such as “43% below today by 2030” can be met by cutting the same percentage every year (compound) or the same tonnage every year (linear). The compound rate is 1 − (1 − target)^(1/years); the linear cut is the total tonnage divided by the years. Cumulative emissions along the path are what the atmosphere sees: the compound path takes a fixed percentage of a still-large base in the early years, so it removes more tonnes early and emits less in total than the straight line.
Formula: yearly % = 1 − (1 − cut)^(1 ÷ years); linear tonnes per year = E₀ × cut ÷ years
Worked examples
| Inputs | Required yearly cut (compound) | Note |
|---|---|---|
| 43% by 2030 from 2026 | 13.11 % | 13.1% a year |
| Halve by 2030 from 2020 | 6.7 % | 6.7% a year |
| 90% by 2050 from 2025 | 8.8 % | 8.8% a year |
FAQFrequently asked questions
Compound or linear — which is right?
Neither is mandated; targets are usually stated as an end point. The compound path cuts more tonnes in the early years (the same percentage of a larger base) and so emits less in total, which matters for the climate; the linear path is gentler at the start in percentage terms and harder at the end.
What is a science-aligned rate?
For a 1.5 °C pathway, roughly 4–8% a year across the economy this decade, halving by 2030 from 2019 levels. Company targets under the Science Based Targets initiative use about 4.2% a year linear for scope 1 and 2.
Why do cumulative emissions matter?
Warming tracks the total carbon ever emitted, not the rate in any one year. Two paths ending at the same target can put quite different amounts into the atmosphere on the way.
What about net zero?
A 100% reduction means the yearly cut reaches the whole of what is left in the final year. Most net-zero plans reduce 90–95% and remove the rest, so enter the reduction share and treat the remainder as removals.
Where these figures come from
- UK DESNZ / DEFRA — Greenhouse gas reporting: conversion factors — the flight, fuel and waste emission factors used here
- Scarborough et al. (2014), Climatic Change — Dietary greenhouse gas emissions — the per-diet daily emission figures
- US EPA — Technical Assistance Document for the Reporting of Daily Air Quality (AQI) — the PM2.5 breakpoints the air quality calculator uses
- US EPA — Greenhouse Gas Equivalencies Calculator — the official US equivalency factors
Last checked: September 2026. Factors are taken from published government and peer-reviewed sources, each named on the page with its year.