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Use a 2, 3, or 5 tCO2e/year comparison lane, or enter a custom target.
Enter a positive target and choose tonnes or kilograms CO2e.
Home energy
Choose the basis that matches the electricity, gas, and heating-oil values below.
Enter the number of residents sharing the whole-house energy totals.
Use average monthly kWh from the same bill basis selected above.
kWh/month
Enter 0 when the home uses no natural gas.
therm/month
Enter 0 when the home uses no oil or diesel heating.
L/month
Travel
Choose one vehicle path to prevent double counting.
Enter annual passenger-kilometers, including all legs.
passenger-km/year
Enter annual bus and rail passenger-kilometers.
passenger-km/year
Food and other
Choose the nearest pattern or use Custom with the factor in Advanced.
Add an annual estimate for purchases, services, pets, or other sources not modeled above.
kgCO2e/year
Leave 0 unless you deliberately want a net scenario.
kgCO2e/year
Applies to home electricity and EV charging.
kgCO2e/kWh
kgCO2e/therm
kgCO2e/L
people
kgCO2e/US gal
kgCO2e/pkm
{{ formatNumber(rf_multiplier, 1) }}×
1.0 keeps direct flight CO2e only; higher scenarios apply an explicit non-CO2 uplift.
kgCO2e/pkm
Factor defaults are editable scenario assumptions; replace them with a documented local or inventory value when available.
kgCO2e/day
SourceAnnual CO2eGross shareBasisCopy
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Gross footprint{{ formatTonnes(computation.values.gross_kg) }}100%Before offsets
Net footprint{{ formatTonnes(computation.values.net_kg) }}{{ formatPercent(computation.values.coverage_percent) }} of budgetGross minus offsets, floored at zero
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Priority checks
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Model boundary

This is a browser-local planning estimate. Editable factor defaults and comparison lanes are not a certified inventory, official allowance, offset validation, or lifecycle assessment.

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Flight Emissions Tracker Estimate flight CO2e from airport codes or manual distances and compare cabin, fuel and radiative-forcing scenarios with a leg-by-leg audit.
Appliance Energy Cost Calculator Estimate an appliance's monthly and annual electricity cost from measured or rated power, runtime, duty cycle, standby use and your local rate.
Heat Pump Savings Calculator Estimate heat pump operating savings and simple payback using fuel use and seasonal efficiency, with utility rates and backup heat included.
EV Range Calculator Estimate reserve-aware EV range from usable battery energy and route consumption, then check trip margin and modeled arrival charge.

Two footprint totals are comparable only when they count the same kinds of activity over the same period. Electricity, heating fuel, travel, food, purchases, and offsets can all be described in carbon dioxide equivalent, but the final number still depends on where the boundary is drawn and which emission factors are used.

Carbon dioxide equivalent (CO2e) expresses the warming effect of different greenhouse gases on one scale. Each source is estimated by multiplying an activity amount by a factor such as kilograms CO2e per kilowatt-hour, litre, gallon, passenger-kilometre, or day. Local electricity generation, fuel composition, vehicle efficiency, route, occupancy, and food production can therefore change the estimate even when the visible activity looks similar.

Decision What it controls Common error
Inventory boundary Which household and personal sources are counted Comparing totals with different omissions
Household allocation How shared utility use is assigned to one person Dividing an already personal value again
Emission factor Estimated CO2e per unit of activity Using a broad average when better local evidence exists
Offsets The difference between gross and net estimates Treating subtraction as a reduction in the original activity

An annual carbon budget is a comparison target, not a precise entitlement or a complete greenhouse-gas inventory. It can show which modeled source is largest, how far a scenario sits above or below a target, and how a change in activity or assumptions affects that gap. Public services, infrastructure, many purchased goods, and supply-chain effects remain outside the estimate unless they are added under other emissions.

Gross emissions preserve the modeled source mix before offsets. Net emissions subtract the entered offset amount but cannot fall below zero. Reduction planning should begin with gross sources because an offset does not change the electricity, fuel, travel, or food activity that produced the estimate.

How to Use This Tool:

Set a comparison target and one consistent annual boundary before adjusting activities or emission factors.

  1. Choose Planning lane. Use 2, 3, or 5 tCO2e/year as a scenario, or enter a positive custom Annual budget in tonnes or kilograms CO2e.
  2. Set Home-energy basis. Choose Shared household bills for whole-home monthly values and enter the resident count. Choose Already my personal share when the utility values have already been allocated.
  3. Select one personal-car path. A combustion car uses annual miles, occupancy, fuel economy, and fuel type. An electric car uses annual miles, occupancy, energy per 100 miles, and the electricity factor. Choose no car to exclude both.
  4. Add annual travel, diet, and other emissions. Flights and transit use passenger-kilometres. Pick a diet scenario or provide a daily factor, then use Other emissions for sources inside your boundary that have no named field.
  5. Replace default factors when better evidence exists. Keep units and time bases aligned. The flight multiplier accepts 1 to 3 and is applied after the direct flight factor.
  6. Compare gross, net, and the budget gap. Add only offsets you intend to treat as verified, then keep the gross source mix visible when choosing reductions.

Interpreting Results:

Coverage is net annual emissions divided by the budget. Exactly 100% uses the full target. Required cut is the positive amount above the target, while Spare budget is the positive amount below it.

Runway months assumes the annual estimate accumulates evenly and caps the answer at 12. It is a pacing comparison, not a forecast of the date when real emissions occur.

Use the largest source as a starting point, then change one activity or factor at a time. A large change after editing a factor measures sensitivity to that assumption; it does not show that real-world activity has changed.

Technical Details:

The model annualizes activity in kilograms CO2e, allocates shared home energy when requested, and keeps full precision through the source totals. Preset targets and diet choices populate values; the equations use the resulting numeric inputs exactly like custom entries.

Formula Core:

Monthly home activity is multiplied by 12 and its factor. Only shared household values are divided by the resident count.

Ehome= Amonth×12×FD

A is monthly electricity, gas, or oil activity; F is its kgCO2e factor; and D is household people for shared bills or 1 for a personal share.

Vehicle paths use different activity units. Occupancy divides the entered annual distance before fuel or electricity is applied.

EICE= milesoccupancy×mpg×Ffuel , EEV= milesoccupancy×kWhPer100mi100×Fgrid
Source Annual calculation
Flights Passenger-kilometres × flight factor × non-CO2 multiplier
Public transit Passenger-kilometres × transit factor
Diet Daily kgCO2e factor × 365
Other Entered annual kgCO2e

Gross emissions add the eight modeled source categories. Net emissions have a zero floor, and a budget entered in tonnes is converted to kilograms by multiplying by 1,000.

Egross=∑source8Esource , Enet=max(0,Egross−Eoffsets) , coverage=EnetB×100
runway=min(12,BEnet/12)

A zero net value returns 12 months. Display formatting rounds the values, while comparisons and later calculations use unrounded results.

Rule Core:

Net coverage Status
< 75%Comfortably under
>= 75% and <= 100%Within budget
> 100% and <= 125%Slightly over
> 125%Over budget

Accuracy and Privacy Notes:

This is a planning estimate with editable factors, not a verified greenhouse-gas inventory or an official personal allocation method. Entries remain in the browser, but copied or downloaded results can reveal household energy use, travel, diet, and other personal activity.

  • Electricity mix, fuel composition, vehicle efficiency, routing, transit mode, and food production vary across places and dates.
  • The 2, 3, and 5 tCO2e targets are comparison scenarios rather than official entitlements.
  • Diet presets describe broad patterns and cannot represent every food, producer, waste rate, or land-use effect.
  • Offset quality, additionality, permanence, leakage, and double counting need review outside this estimate.

Worked Examples:

Shared home and combustion car

A two-person home using 250 kWh of electricity and 20 therms of gas each month assigns 600 and 636 kgCO2e per person under the reference factors. Adding 6,000 gasoline-car miles at 30 mpg, 2,000 flight kilometres, 1,500 transit kilometres, the average diet scenario, and 400 kg of other emissions produces 5,614 kgCO2e for the year. Against a 3,000 kgCO2e budget, coverage is about 187.1%, the required cut is 2,614 kgCO2e, and the result is Over budget.

References: