What Is an Epoch on Cardano? The Five-Day Clock, Explained

Think of a city tram that comes every eight minutes. After a few weeks you stop checking the timetable. You just walk to the stop, and if you miss one, you know the next is close. The rhythm is so regular that you stop thinking about it.

Cardano has a rhythm like that too. It is called an epoch, and it lasts exactly five days. Almost everything on the network follows it: staking, rewards, even voting. Once you understand the epoch, a lot of “why is it taking so long?” questions answer themselves.

What is an epoch?

An epoch is a fixed period of time on the Cardano blockchain. Every epoch is five days long. When one ends, the next one starts right away, day and night, without a break.

Epochs have numbers. The network started counting in September 2017 with epoch 0. When this article goes out, we are in epoch 663. You can see the current number and a countdown on any Cardano explorer, for example CardanoScan.

A new epoch starts at 21:45 UTC. In Poland that is 22:45 in winter and 23:45 in summer. So for a pool operator in Europe, epoch change is an evening event.

What is inside an epoch? Slots

Each epoch is cut into small pieces called slots. One slot is one second. Five days have 432,000 seconds, so every epoch has 432,000 slots.

A slot is a chance to add a new block. A block is a page in the shared record book: a group of transactions that the whole network accepts together.

Most slots stay empty. This is on purpose. Cardano is set up so that, on average, only about one slot in twenty gets a block. That gives the computers around the world time to pass each new block to each other before the next one arrives. In practice, a new block appears roughly every 20 seconds, and an epoch has around 21,600 blocks. The last full epoch before I wrote this, epoch 662, had 21,268.

Who decides who makes the next block?

Before each epoch, the protocol holds a kind of lottery for every slot. The winners are stake pools: computers run by people like me that keep a copy of the blockchain and make blocks.

The more ADA is delegated to a pool, the more “tickets” it has in this lottery. A big pool wins many slots in an epoch. A small pool may win only a few, or sometimes none. That is why small pools have rewards that jump up and down from one epoch to the next, while big pools look smoother. Over a longer time it evens out.

Nobody can see the full list of winners in advance. Each pool only learns which slots it won. This makes it hard for an attacker to know whom to target.

The snapshot: a photo of who holds what

At the start of every epoch, the network takes a snapshot. Think of it as a photo of all the ADA and which pool each wallet is delegated to.

The protocol does not use the newest photo straight away. It waits, so that everybody has the same, settled picture before the lottery. This waiting is the reason for the most common question I get from new delegators.

Why do my first rewards take 15 to 20 days?

Here is the timeline, step by step. Say you delegate your ADA during epoch N.

1. Epoch N: you send your delegation. It is now written on the blockchain.
2. Start of epoch N+1: the snapshot “sees” your stake with the new pool.
3. Epoch N+2: your stake is active. The pool makes blocks with it.
4. Epoch N+3: the network calculates the rewards for epoch N+2.
5. Start of epoch N+4: the rewards arrive in your wallet.

Four epochs of five days each means 15 to 20 days, depending on how early in epoch N you delegated. After that first wait, rewards come every five days, as long as your pool makes blocks. This timeline is also described on the official cardano.org delegation page.

Nothing is lost while you wait. Your ADA never leaves your wallet, you can spend it at any time, and there is no lock. If you want the full basics of staking first, I wrote about them in What is Cardano Staking?.

What if I change pools?

The same clock applies. A new delegation becomes active in the epoch after next. Your old pool still pays you for the epochs where your stake was counted with it, so you get three more payouts from the old pool, then the new pool takes over. There is no gap.

So please do not switch pools every week because one epoch looked bad. With the snapshot delay, by the time your move is active, luck has often changed already.

Epochs and voting

Since the Chang upgrade in September 2024, Cardano also has on-chain governance. Its timing follows epochs too:

• A governance action (a proposal, for example to spend money from the treasury) stays open for voting for 6 epochs, about 30 days.
• A DRep (a person you choose to vote for you) becomes inactive after 20 epochs without voting, about 100 days.

If you want to know more about DReps and how to choose one, see What Is a DRep?.

What an epoch cannot tell you

An epoch is a clock, not a promise. Rewards in one epoch depend on how many blocks your pool won in the lottery, and that is luck in the short term. A pool can do everything right and still have a quiet epoch. Over many epochs the numbers get close to what you would expect, but no pool can tell you exactly what you will earn next week. Anyone who promises that is guessing.

Also, the five days are fixed by the protocol today, but the community could change parameters in the future through governance. It is a rule written in code, not a law of nature.

Why I like the five-day rhythm

For me, as a pool operator, the epoch is like that tram. It is calm and predictable. Every five days, the snapshot is taken, rewards are paid, and a new lottery starts. I check that our block producer is ready for the next epoch, I look at how many blocks we were given, and then I go back to normal life.

For you, as a delegator, the epoch means you can forget about staking most of the time. Delegate once, wait about three weeks for the first reward, then let the clock do its work.