Hard Cap

A hard cap is a fixed upper limit that cannot be exceeded. In crypto the term has two meanings. In fundraising, it is the most money a project will accept in a token sale; once it is reached, the sale closes. In monetary design, it is the maximum number of coins or tokens that can ever exist, the best-known example being Bitcoin's limit of just under 21 million.

The fundraising hard cap is usually paired with a soft cap, the minimum a sale must raise to go ahead. The supply hard cap is the "maximum supply" shown on data sites, the ceiling above total supply and circulating supply. Both are set by the project's code or terms, not by any regulator.

A concert hall has a fire-safety limit: once 2,000 people are inside, the doors close, however long the queue. A token sale's hard cap works the same way. The organisers decide in advance the most money they will take, and when that figure is hit, nobody else gets in.

The second meaning is like a limited-edition print run. The artist promises there will only ever be 500 copies and destroys the printing plate. A supply hard cap is that promise written into software: however popular the coin becomes, no more than the stated number can ever be made.

During the 2017 boom in initial coin offerings (ICOs), many sales were uncapped and raised far more than their stated plans needed. Hard caps became a way to show restraint and to limit how much of the token supply investors could buy. The cap is normally set in a base currency, such as ether or US dollars, and enforced by the sale's smart contract, which rejects payments once the limit is reached.

A tight cap combined with strong demand often produces a sale that sells out in seconds. Brave's Basic Attention Token sale on 31 May 2017 raised about $35 million in under 30 seconds, and press reports at the time noted that a small number of addresses bought most of the tokens. Episodes like this led projects to add a whitelist, per-wallet limits and lotteries, and later to move sales onto exchange platforms through initial exchange offerings (IEOs) and onto DEX launchpads as initial decentralized offerings (IDOs).

The cap matters for valuation. If a sale offers a set share of supply, the hard cap fixes the implied valuation of the whole network:

• $V$ is the implied valuation of all tokens at the sale price.
• $H$ is the hard cap, the most the sale can raise.
• $f$ is the fraction of total tokens offered in the sale.

Worked example: a sale with a hard cap of $20 million that sells 10% of all tokens implies a valuation of $20 \div 0.10 = 200$ million dollars, comparable to the fully diluted valuation at the sale price.

Bitcoin (BTC) has no line of code that says "21 million". The limit follows from its issuance rule: the block reward began at 50 BTC and halves every 210,000 blocks. Summing that series gives the cap:

Here $S_{\max}$ is the maximum supply, 210,000 is the number of blocks between each halving and 50 is the starting reward. Because rewards are rounded down to whole satoshis, the real ceiling is slightly below 21 million; the 21 million bitcoins entry covers the details.

Many tokens copy the idea with a maximum written into the contract. Others, including Ethereum (ETH), have no hard cap and rely on fee burning to limit growth. A hard cap is a design choice that links to the debate over inelastic supply as a form of sound money versus an elastic supply that can respond to demand.

• Caps can be changed. A supply cap holds only as long as the community refuses to adopt a hard fork that alters it, and a contract owner who keeps a mint function can ignore a stated cap.
• Fundraising caps do not guarantee fairness. Sales that sell out instantly reward bots and large buyers, and pre-sale rounds for insiders may already have sold tokens below the public price; see token pre-sale.
• Regulation still applies. The U.S. Securities and Exchange Commission (SEC) has treated many capped token sales as securities offerings under the Howey Test; a cap does not change that analysis.
• A fixed supply is not a guarantee of value. Scarcity helps only if there is demand, and fixed-supply tokens can still lose most of their value.

Readers comparing projects usually check both meanings: how much a team raised against its hard cap, and whether the token's maximum supply is enforced by code or only promised in a whitepaper. The project's broader tokenomics show how the capped supply is shared out over time.

• Bitcoin: A Peer-to-Peer Electronic Cash System
• U.S. Securities and Exchange Commission: Crypto Assets