How quickly does Bitcoin’s user community grow? Few questions in Bitcoin are more important – or difficult to answer. The rate of user growth figures prominently in areas ranging from the evaluation of scaling solutions to the allocation of investor capital. Some ways to estimate this important metric are discussed here.

Although the block chain can offer insights into user behavior, this information is limited by design. One factor is the block size limit, which imposes an upper bound on transaction throughput. This limit was reached in mid-2016.

Even without a block size limit, pseudonymity thwarts the analysis of those transactions that are published. Savers, who make few transactions, tend to generate few pseudonyms. Merchants, who make many transactions, may generate thousands of pseudonyms. In neither case is it clear whether a pseudonym represents a single user or thousands of them.

With the advent of full blocks and ongoing research into secure off-chain scaling solutions such as Lightning Network, the role of on-chain transactions as a measure of economic activity will only decline. For these reasons, estimation of user growth needs to account for both on-chain and off-chain applications.

Coinbase

Shortly after its founding in 2012, Coinbase’s About page began publishing a “Users” metric. The company offers no historical data, but a time series can nevertheless be reconstructed from the Wayback Machine.

Inspection of this data set reveals that Coinbase’s user count has doubled roughly once every year since it was founded. If this trend holds, Coinbase’s user count one year from today (October 10, 2018) will stand at 21,600,000.

SVG Image Coinbase User Growth. User count has doubled roughly once every year since the company was founded.

As discussed previously, Coinbase doesn’t reveal whether its “Users” count includes AML/KYC-approved users or merely users who signed up for an account.

Blockchain.info

Blockchain.info reports historical wallet count data. From its founding in late 2011, the number of wallets created has roughly doubled once every year. If this trend holds, the number of Blockchain wallets will total 35,000,000 within one year.

SVG Image Blockchain Wallets. The number of Blockchain wallets has doubled roughly once every year.

As noted previously, creating a blockchain wallet is quick and easy, and doesn’t even require email verification. As such, it’s difficult to assign specific meaning to the number of wallets. Nevertheless, the approximate doubling of the wallet count every year matches the growth rate of Coinbase users.

Reddit

Reddit’s /r/bitcoin subreddit is an important information resource and discussion forum. Subscribers receive its posts on their main page view. Although Reddit publishes subscriber growth metrics, this service often doesn’t work. The Wayback Machine can be used to compile subscriber growth statistics in the same manner that Coinbase’s user growth series was compiled.

SVG Image Reddit Subscribers. Strong growth periods are punctuated with periods of almost no growth that coincide with major exchange rate corrections.

Unlike the previous graphs, this one shows two major strong/weak growth periods that track major exchange rate moves. Some periods (e.g., September 2015 through September 2016 show almost no subscriber growth) whereas others (e.g., September 2016 through September 2017) show explosive growth.

Although these results qualitatively match the steep upward-and-to-the-right trajectory of the other graphs, Reddit subscriber growth is much more closely correlated with exchange rate fluctuations. Overall, a doubling rate somewhat longer than one year appears feasible.

Google Trends

Willy Woo has advocated Google search frequency for the term “BTC USD” as a user growth metric. Using this particular term makes sense, according to Woo, because Bitcoin users are likely to be more interested in exchange rate quotes than non-users. From analysis of Google’s data, Woo concluded that the Bitcoin user base doubles in size every year, dubbing the phenomenon “Woo’s Law.”

SVG Image Google Searches. Bitcoin users are more likely than anyone else to search the term “BTC USD.” As such, the increase in this search term’s frequency might be expected to track user growth rate. Google notes a change of reporting method on January 1, 2016.

Plotting the data obtained from Google Trends reveals large fluctuations within an expanding envelope. Whether use of Woo’s specific search term doubles every year is debatable. Like Bitcoin subreddit subscriber growth, the data show prolonged discontinuity. For example, the period from September 2014 through September 2015 showed little to no growth at all. In contrast, the period from September 2016 through September 2017 saw search frequency nearly quintuple. Nevertheless, an overall doubling rate of roughly once every year seems plausible.

UTXO Set

Although the block chain imposes limits as a user growth gauge, one metric in particular deserves attention. The unspent transaction output (UTXO) count represents the number of unspent coins. (Recall that Bitcoin is an electronic cash system.) The absolute coin count probably doesn’t equate to the number of users because one user can control multiple coins, and one coin can be collectively controlled by many users. But assuming constant usage patterns, the growth rate of the UTXO set should correlate with the rate of user growth.

UTXO Set. Changes in the number of unspent coins might be expected to track changes in user base size.

A graph of the UTXO set size versus time can be obtained from statoshi.info. From this graph, a doubling time of roughly one year is apparent until mid-2016, at which point the rate slows. This deceleration coincides with the advent of full blocks in mid-2016 and the resulting sharp increase in network fees.

Eternal September

“Eternal September” refers to the continuous influx of new users experience by the Internet discussion system Usenet starting in September 1993. Until that point, Usenet access had been restricted mainly to university campuses. The start of each new school year would bring a flood of new users composed mainly of the incoming freshman class. In September 1993, however, Internet Service provider AOL began offering Usenet access to its home subscribers. Whereas newbie questions and cultural transgressions previously occurred on an annual basis, they immediately became a permanent fixture of Usenet life.

Eternal September can happen to any network experiencing exponential user growth. As the graphs in this post reveal, Bitcoin shows the numerical symptoms of Eternal September. One important implication would be that at any moment roughly half of all Bitcoin users will have less than one year of experience. Given the difficulty of securing bitcoin, many new users will turn to trusted third parties to do it for them, increasing centralization pressure.

The possible link between Usenet’s Eternal September and the one apparently unfolding around Bitcoin has been noted previously.

World Domination

Assuming that the Bitcoin user community doubles in size once every year, at what point will every human be a Bitcoin user? The idea that Bitcoin could become a ubiquitous world currency is not new, and has been hotly debated for years. What’s often missing from these discussions, however, are the answers to two fundamental questions:

What is the current size of the Bitcoin user community? How fast is this community growing?

The answer to question (2) has just been estimated at roughly 100% per year, a claim supported by the data presented in this post. This leaves current size of Bitcoin’s user base.

2017 Global Cryptcurrency Benchmarking Study from Cambridge University attempted to answer question (1) in the broader context of cryptocurrency users, concluding:

Using data obtained from study participants and assuming that an individual holds on average two wallets, we estimate that currently there are between 2.9 million and 5.8 million unique users actively using a cryptocurrency wallet. …

Although Bitcoin user base figures aren’t specifically reported, controlling bitcoin in some form is required to trade into or out of most cryptocurrencies. As such, it’s plausible that the majority of cryptocurrency users are also Bitcoin users, at least transiently.

The Cambridge report also provides a time series indicating that the cryptocurrency user count doubles on a somewhat longer time horizon than one year.

Cryptocurrency User Growth. Estimated cryptocurrency user count as a function of time. This figure was published in 2017 Global Cryptocurrency Benchmarking Study.

As a lowball estimate for the current size of Bitcoin’s user community, assume that only 25% of currently active cryptocurrency users also use Bitcoin. Accepting the Cambridge report’s midpoint value for 2017 (4.3 million) would imply a Bitcoin user base of 1.1 million.

Combining this value with Bitcoin’s user growth rate allows an estimate of the year in which every person on Earth will use Bitcoin. According to the United Nations, world population as of 2017 stood at 7.6 billion. Assuming that the current number of Bitcoin users stands at 1.1 million and doubles every year, we can expect every person on Earth to be a Bitcoin user by 2030 (13 years from now).

SVG Image User Growth Projection. An unrealistic extrapolation of current exponential user growth trends.

Few population growth rates look like this over the long term because exponential growth depletes scarce resources, stunting growth. Instead, population growth curves tend to appear S-shaped, following a logistic function. Many factors could dampen Bitcoin’s current exponential user growth rate. On the technical side, Bitcoin faces numerous accessibility and usability issues that extend far beyond the block size limit. As Bitcoin becomes more commonplace, it will be resisted viciously by many governments interested in maintaining currency monopolies. Technical and political headwinds aside, Bitcoin’s success has already spawned an army of altcoin competitors, each of which fights over a similar user base and capital pool. Competition for these resources will only increase as Bitcoin’s user community grows.

Scaling Bitcoin

The first public question Satoshi received after publishing his white paper related to scaling. Since 2015, this single topic has dominated discussion in the developer and user communities. A recent article attempted to address the question of how Bitcoin could support, not every living human, but only one billion of them. The author concluded that the cost of doing so given the current state of the art would be “astronomical.”

Rational scaling of access to any resource requires knowing both the current user count and a likely future growth rate. Only with reliable data on both metrics do discussions about scaling technologies and Bitcoin’s long-term viability make sense. Unfortunately, all of the estimates for user count and growth reported in this article are flawed — perhaps fatally so.

Trying to estimate user growth anyway offers three benefits. First, the metrics reported here can offer insights into user behavior over time, even if interpretation is difficult. Second, analyzing the faults of an existing metric may lead to better metrics. Finally, the user statistics presented here, despite their flaws, consistently point to an expanding economy that under ideal conditions will play a major role on the world stage within the lifetimes of most current users.