Earth Overshoot Day Calculator
Overshoot date and Earths from footprint math.
What it does
Overshoot Day marks when demand passes yearly supply: biocapacity over footprint times 365 days. A 2.7 footprint against 1.6 biocapacity lands day 216, August 4, needing 1.69 Earths. Smaller gaps push the date toward December; balance erases it.
The tool above runs the Global Footprint Network formula on a 2026 calendar. Enter footprint with biocapacity in global hectares per person, and it prints day number, date, and Earths. Balanced inputs land Dec 31 with 1 Earth; heavy footprints pull spring dates.
The Network publishes the method openly. Its media formula divides biocapacity by footprint times 365 from National Footprint Accounts on UN data, with 2025 falling July 24. WWF corroborates the footprint framework through calculators and Living Planet reports.
Editions revise history yearly, so cross-year comparisons need matching accounts. Footprint mixes carbon, food, fiber, and built land into one hectare ledger; composition shifts real pressure behind single dates. Treat the day as an indicator, not an appointment.
How to use
- Enter footprint in gha/person.
- Enter biocapacity in gha/person.
- Read the day number first.
- Read the calendar date.
- Read Earths needed.
- Compare same editions only.
Formula
- footprint
- Demand in global hectares per person.
- biocapacity
- Supply in global hectares per person.
Global Footprint Network media formula with floor convention; same-year same-edition comparisons only.
Worked example
Example: 2.7 over 1.6
Defaults: 2.7 footprint, 1.6 biocapacity.
- Inputs: 2.7 footprint, 1.6 biocapacity gha.
- Earths: 2.7 / 1.6 = 1.69.
- Raw day: 1.6 / 2.7 x 365 = 216.30.
- Floor to day 216: August 4 (2026 calendar).
- Tool shows day 216, Aug 4, 1.69 Earths.
Reference table
| Footprint | Day | Earths |
|---|---|---|
| 1.6 | 365 (Dec 31) | 1.00 |
| 2.7 | 216 (Aug 4) | 1.69 |
| 2.75 | 212 (Jul 31) | 1.72 |
| 3.5 | 166 (Jun 15) | 2.19 |
| 5.0 | 116 (Apr 26) | 3.13 |
Limits
- Indicator math only. Composition ignored.
- Same edition/year comparisons only.
- Non-leap calendar fixed.
- Policy needs full accounts.
Common mistakes
- Mixing account editions across years.
- Reading the date as exact.
- Ignoring footprint composition.
- Comparing unbalanced ledgers.
- Treating 1 Earth as headroom.
Try it yourself
Quick checks. Answers sit tucked under each question.
Footprint 1.6, biocap 1.6?
Earths 1.6/1.6 = 1. Raw day 365. Date Dec 31, no overshoot.
Footprint 5.0, biocap 1.6?
Earths 5/1.6 = 3.13. Raw 1.6/5 x 365 = 116.8, floor 116. Date Apr 26.
Questions
How is the day figured?
Biocapacity over footprint times 365, floored. Here 216.30 floors to day 216.
How many Earths?
Footprint over biocapacity. Here 1.69 Earths.
What date is day 216?
Day 216 on the 2026 calendar: July holds 212, so 216 minus 212 = Aug 4.
What if footprint meets biocapacity?
Day 365 lands Dec 31 with no overshoot that year.
Can years compare directly?
Same year with same accounting edition only; editions revise history yearly.
Is the date exact?
Yes. The date approximates; footprint mix shifts real pressure behind single dates.