What is the Lightning Network? Fast, cheap Bitcoin payments

The Lightning Network is a system built on top of Bitcoin for fast, cheap payments. Instead of writing every payment to the blockchain, two people lock some bitcoin into a shared account called a payment channel, then pay each other as often as they like by updating who owns how much. Only the opening and the final balance go on the blockchain. Payments can also hop across a chain of channels, so you can pay people you have no channel with.

In short

• Bitcoin's main chain adds a block about every ten minutes and fits only a handful of payments a second, so small payments there are slow and can be costly.
• A Lightning channel turns many payments into two blockchain transactions: one to open it and one to close it.
• The trade-offs are real: channels need funds on the right side, software that stays online, and many apps hold the keys for you.

Why does Bitcoin need a second layer?

Because the base chain is built to be checked by everyone, and that limits its speed. A new block arrives about every ten minutes, and each block holds a limited amount of data, so the network as a whole confirms only a handful of payments a second. In their 2016 Lightning Network paper, Joseph Poon and Thaddeus Dryja put it at fewer than 7 transactions a second, against 47,000 a second that Visa handled at its peak in the 2013 holidays. When more people want to pay than blocks can hold, they bid for space with fees, which can cost more than a small payment is worth.

Making blocks much bigger would raise the cost of running a node, the computer that checks every rule, until only large companies could afford it. The Bitcoin community largely chose a different path: keep the base layer small and checkable by anyone, and build faster systems on top. Lightning is the best known. It needed a fix to how Bitcoin transactions are identified, which arrived with the SegWit upgrade in 2017, and the first Lightning software meant for Bitcoin's main network was released in 2018.

How does one payment channel work?

A channel is a shared pot that two people can only spend together. Here is one, step by step, with Alice and a coffee shop run by Bob. Amounts are in satoshis, or sats; 100 million sats make one bitcoin.

1. Opening. Alice puts 1,000,000 sats into a Bitcoin address that needs both her signature and Bob's to spend. That funding transaction goes on the blockchain like any other payment, with one ordinary fee.
2. Paying. Each morning Alice buys a coffee for 20,000 sats. She doesn't send anything to the blockchain. She and Bob both sign a new version of a transaction that would split the pot: Alice 980,000, Bob 20,000. The next day they sign Alice 960,000, Bob 40,000. Each update takes about as long as sending a message.
3. Keeping score. After ten coffees, the latest signed version says Alice 800,000, Bob 200,000. Either of them could put it on the blockchain at any moment and get their share, so neither has to trust the other.
4. Closing. When they are done, one final transaction pays Alice 800,000 and Bob 200,000 on the chain.

Ten payments, two blockchain transactions. With a hundred or a thousand payments, the saving grows, and the chain never sees the individual coffees.

	On-chain payment	Payment in a Lightning channel
Written to the blockchain	Every payment	Only the opening and the closing
Time to be final	Usually several blocks, tens of minutes	Seconds
Fee	Set by demand for block space	Usually tiny, plus the on-chain fees to open and close
Who can see it	Anyone, forever	Mainly the people in the channel and the route

What stops Alice cheating by publishing the old version from the first morning, when she still had all 1,000,000? Each time they sign a new version, each hands the other a key that cancels their own old ones. If Alice publishes a cancelled version, Bob has a window, set as a number of blocks, to use that key and take everything in the channel. Cheating is possible, but it risks losing the whole pot. That penalty only works if Bob, or a service he hires to watch for him, called a watchtower, is checking the blockchain.

How do payments travel across the network?

Alice doesn't want a channel with every shop. If she has a channel with Bob, and Bob has one with Carol, Alice can pay Carol through Bob. The difficulty is making sure Bob can't keep the money in the middle. Lightning solves it with a hash time-locked contract, or HTLC, a payment that can be claimed only by revealing a secret, before a deadline, as Bitcoin Optech describes.

Say Alice owes Carol 50,000 sats:

1. Carol picks a random secret and sends Alice its fingerprint, a hash, inside an invoice. A hash is easy to compute from the secret and practically impossible to reverse.
2. Alice offers Bob 50,001 sats in their channel, payable only if Bob reveals the secret that matches the hash within, say, 40 blocks.
3. Bob offers Carol 50,000 sats in their channel on the same condition, but within 20 blocks, a shorter deadline.
4. Carol reveals the secret to Bob to claim her 50,000. Bob now knows the secret and uses it to claim 50,001 from Alice, keeping 1 sat as his fee.

Either everyone along the route gets paid, or the deadlines pass and every offer is cancelled. Bob never holds Alice's money in a way he could run off with. The shorter deadline for the later hop gives Bob time to claim from Alice after Carol claims from him. Real payments often cross three or more hops, and software finds the route. The signatures that make all of this enforceable rest on public-key cryptography.

What are the trade-offs?

Lightning is fast and cheap because it asks more of its users than the base chain does.

• Liquidity. A channel can only move money toward the side that has room. Bob can't receive more from Alice than the 1,000,000 sats in their pot, and a new user with a fresh channel often can't receive at all until someone puts funds on the other side. Large payments can fail when no route has enough on the right sides.
• Staying online. To receive a payment, your software must be online, and to catch cheating, you or a watchtower must keep an eye on the chain.
• Custody. Running your own channels takes care, so many popular apps run them for you and hold the keys. That is easier, but it is like leaving coins on an exchange: the app holds the bitcoin and you hold a claim on the app. The crypto wallet note explains why that matters.
• On-chain costs don't vanish. Opening and closing channels are ordinary Bitcoin transactions, so when fees on the main chain are high, so is the cost of getting in and out.

How big is the network?

The public part is easy to count; the rest isn't. In early November 2026, the mempool.space explorer counted about 16,200 public Lightning nodes with about 32,500 channels between them, holding a combined 3,754 bitcoin. Those numbers leave out private channels, which aren't announced, and they change week to week. The rules all the main programs follow are published openly as the BOLT specifications, so different implementations can open channels with each other.

Still argued

Whether Lightning can carry everyday payments for very large numbers of people is argued among Bitcoin developers. Supporters point to fast, cheap payments that work today without any change to Bitcoin's base rules. Critics point to the liquidity and online requirements, to how much use runs through custodial apps, and to the on-chain cost of opening a channel for each new user if fees rise. This note explains how it works; it isn't financial advice.

Lightning doesn't change how bitcoin itself is created or secured; that still happens through mining on the base chain, which every channel ultimately falls back on.

Check yourself

• Walk through a channel between two people from opening to closing, and say which steps touch the blockchain.
• Why can't the middle person in a routed payment keep the money?
• What is inbound liquidity, and why can a new Lightning user have trouble receiving a payment?

Sources

• The Bitcoin Lightning Network: Scalable Off-Chain Instant Payments — Joseph Poon and Thaddeus Dryja, 2016
• BOLT: Basis of Lightning Technology specifications — Lightning developers, GitHub
• Hash Time Locked Contracts (HTLCs) — Bitcoin Optech
• Lightning Network explorer — mempool.space, 2026
• Block chain, in the Bitcoin developer guide — Bitcoin Project
• Lightning Network — Wikipedia