This calculator works through the Drake Equation, the seven-factor formula astronomer Frank Drake proposed in 1961 to estimate N, the number of technologically advanced civilisations in the Milky Way whose signals we could currently detect. You enter each factor yourself, or choose a preset scenario, Drake's original 1961 figures, an optimistic case, a pessimistic case, or a modern Kepler-informed case, then adjust any of the seven inputs: the rate of star formation, the fraction of stars with planets, the average number of habitable planets per star, the fraction of habitable planets that develop life, the fraction that develop intelligence, the fraction that release detectable signals, and how many years such signals continue. The calculator multiplies these together and returns the estimated N, plus supporting figures showing how many habitable planets form each year, how many civilisations ever arise each year before the signal-lifetime factor is applied, and a rough nearest-neighbour distance if civilisations were spread evenly across the galaxy. A full breakdown lists each factor alongside a plain-English summary of what your result implies. Because the last four factors rest on a single data point, Earth, treat any figure you get as an illustration of your own assumptions rather than a scientific prediction; small changes to the more speculative factors can shift N by orders of magnitude.
The Drake Equation estimates N, the number of technologically advanced civilisations in the Milky Way galaxy whose electromagnetic signals we could currently detect. Frank Drake wrote it in 1961 ahead of the first major SETI (Search for Extraterrestrial Intelligence) conference at Green Bank Observatory, not as a proven formula but as a way of breaking an impossibly large question into seven smaller, more tractable questions. Multiplying the seven factors together gives:
N = R* × fp × ne × fl × fi × fc × L
| Symbol | Meaning | How well known? |
|---|---|---|
| R* | Average rate of star formation in the galaxy, per year | Reasonably well measured by astronomers |
| fp | Fraction of those stars that have planets | Well constrained since the Kepler mission; most stars have planets |
| ne | Average number of planets per star that could support life | Increasingly well estimated from exoplanet surveys |
| fl | Fraction of habitable planets that actually develop life | Unknown, based on a sample size of one (Earth) |
| fi | Fraction of life-bearing planets that develop intelligent life | Unknown, highly speculative |
| fc | Fraction of intelligent civilisations that release detectable signals into space | Unknown, highly speculative |
| L | Length of time such civilisations continue to release detectable signals, in years | Unknown; depends on the long-term survival of technological societies |
Because all seven terms are multiplied together, the Drake Equation is extremely sensitive to the least certain inputs. The first three factors (R*, fp, ne) are now grounded in real astronomical data, largely thanks to NASA's Kepler space telescope, which confirmed that planets are common around other stars. The last four factors (fl, fi, fc, L) remain essentially guesses, since we have only one confirmed example of life anywhere in the universe: Earth. Depending on the assumptions chosen, published estimates for N have ranged from a small fraction (implying humanity may be alone or nearly so) to many millions.
At the founding SETI meeting, Drake used illustrative values of R* = 10 stars per year, fp = 0.5, ne = 2, fl = 1, fi = 0.01, fc = 0.01, and L = 10,000 years, which multiply out to N = 10. This calculator loads those original figures by default, matching Drake's own worked example, and lets you adjust any factor from there. Drake himself was clear that the equation's main value is in organising scientific ignorance into named categories that can be individually researched and refined over time, not in producing a single confident number.
Sources: Drake, F. (1961), Green Bank Conference on Extraterrestrial Intelligent Life. NASA SETI Institute overview of the Drake Equation (seti.org). NASA Exoplanet Archive and Kepler mission results (exoplanets.nasa.gov).
The Drake Equation is a framework for structuring an unanswered scientific question, not a validated formula with measured inputs. The last four factors are speculative and any resulting value of N should be treated as illustrative only, not a scientific prediction.
The Drake Equation is a probabilistic argument written by astronomer Frank Drake in 1961 to estimate the number of active, communicating extraterrestrial civilisations in the Milky Way galaxy. It multiplies seven factors together: the rate of star formation, the fraction of stars with planets, the number of habitable planets per system, the fraction of those that develop life, the fraction of life that becomes intelligent, the fraction of intelligent civilisations that develop detectable communication technology, and the length of time such civilisations release detectable signals. It is not a strict scientific formula with proven inputs, but a framework for organising the unknowns.
Most of the seven factors cannot be measured directly and rely on assumptions. The star formation rate and fraction of stars with planets are now reasonably well constrained by astronomical surveys, but the fraction of habitable planets that develop life, develop intelligence, and develop detectable technology are essentially guesses. Because the equation multiplies all seven values together, small changes in the more speculative factors change the final result by orders of magnitude. Estimates in published literature range from far less than 1 to many millions.
At the 1961 Green Bank meeting, Drake and colleagues used illustrative values including a star formation rate of about 10 per year, a fraction of stars with planets of 0.5, an average of 2 habitable planets per system, a fraction developing life of 1, a fraction developing intelligence of 0.01, a fraction developing detectable technology of 0.01, and a civilisation communication lifespan of 10,000 years. These particular numbers gave a result of roughly 10 communicating civilisations, but Drake always described them as a starting point for discussion rather than a firm prediction.
If you've found a bug, or would like to contact us, or learn more about James Graham and Calculate.co.nz.
Calculate.co.nz is partnered with Interest.co.nz for New Zealand's highest quality calculators and financial analysis.
Calculate.co.nz is the sister site of CalculatorHub.com, the world's largest calculator website by tool count.
All calculators and tools are provided for educational and indicative purposes only and do not constitute financial advice.
Calculate.co.nz is proudly part of the Realtor.co.nz group, New Zealand's leading property transaction literacy platform, helping Kiwis understand the home buying and selling process from start to finish. Whether you're a first home buyer navigating your first property purchase, an investor evaluating your next acquisition, or a homeowner planning to sell, Realtor.co.nz provides clear, independent, and trustworthy guidance on every step of the New Zealand property transaction journey.
Calculate.co.nz is also partnered with Health Based Building and Premium Homes to promote informed choices that lead to better long-term outcomes for Kiwi households.
Calculate.co.nz is hosted in Auckland by SiteHost New Zealand.
All content on this website, including calculators, tools, source code, and design, is protected under the Copyright Act 1994 (New Zealand). No part of this site may be reproduced, copied, distributed, stored, or used in any form without prior written permission from the owner.
About & trust: Why Calculate is NZ's most comprehensive · By the Numbers · How we compare · Editorial standards · How we keep data current · NZ finance glossary · Research & data · Financial literacy NZ · About · Privacy policy · Terms of use
Reviewed and maintained. Last reviewed 2026-08-15 and checked on a twice-monthly cycle against IRD, RBNZ and Stats NZ. How we keep data current.
© 2026 Calculate.co.nz. All rights reserved. Building free NZ calculators since 2011.