The Coinbase Transaction Explained: How a Solo Block Reward Reaches Your Wallet

The Coinbase Transaction Explained: How a Solo Block Reward Reaches Your Wallet

If you have ever opened a found block on a public explorer, you will have seen something odd at the top of the transaction list: a transaction with no normal sender, creating bitcoin out of nothing. That is the coinbase transaction. For a solo miner it is the single most important transaction in the block, because it is the one that carries the reward. Understanding it makes block finds, payouts, and explorer pages far less mysterious.

The coinbase transaction is the first transaction in every Bitcoin block. It has no real inputs — instead of spending existing coins, it creates the block reward: the block subsidy (currently 3.125 BTC since the April 2024 halving) plus the transaction fees from that block. Coinbase outputs cannot be spent until they have 100 confirmations, a rule called coinbase maturity. The coinbase transaction also holds the extranonce space your miner rolls when its nonce range runs out. In solo mining the reward is built for the find, so the payout wallet behind your WALLET.worker matters. Bitmern Solo charges a flat 1% on finds — you keep 99%. The term has nothing to do with the exchange company of the same name. Keep BTC easy-start host btc.bitmernsolo.com with port :3132 (never treat :3102 as the Bitaxe / home default), username WALLET.worker, password x. Current Effort is not a find guarantee.

This is the "how the reward is created" lane. The moment of a find is covered in what happens when you find a block. How and when Bitmern Solo payouts arrive is in payout timing, and confirming one on-chain is in verify payout on an explorer.

Bitmern Solo is solo infrastructure: flat 1% fee on finds only, you keep 99%. Nothing in this post is financial advice, and nothing here promises a find.

First, a naming note

"Coinbase" in this post means the coinbase transaction — a term from Bitcoin's original design for the transaction that creates new coins. It is unrelated to the exchange company called Coinbase. Same word, different thing.

What the coinbase transaction is

Every Bitcoin block contains a list of transactions. The first one is always special:

1. It is created by the miner who builds the block. No user sends it.
2. It has no real inputs. Normal transactions spend coins from earlier transactions. The coinbase transaction has a placeholder input instead, because the coins it pays out are new.
3. It pays the block reward. Its outputs carry the subsidy plus the fees from every other transaction in the block.
4. There is exactly one per block. A block without a valid coinbase transaction is not valid.

Because it is part of the transaction list, it is also part of the merkle root in the block header. Change the coinbase transaction and the header changes — which is exactly why it matters for mining.

What the block reward is made of

The coinbase transaction pays out two things:

1. The block subsidy. New bitcoin set by protocol rules. It is currently 3.125 BTC per block, since the April 2024 halving. The subsidy halves on a fixed block schedule — see halving explained.
2. Transaction fees. The total fees from all the other transactions included in that block. These vary block to block.

The coinbase outputs can claim up to subsidy + fees. That total is what people mean by "block reward".

Why the coinbase transaction matters in solo mining

In pool mining, a pool combines many miners' work and shares rewards out over time. In solo mining, the trade is different: a find is the whole block reward for that block, not a slice of pooled earnings.

That means the block your miner is working on is built so the reward goes toward the find. Two practical consequences:

1. Your payout wallet matters before a find, not after. The wallet behind WALLET.worker is how Bitmern Solo knows where your reward should go. Make sure it is a valid address you control — see invalid wallet rejects and change payout wallet.
2. The fee is simple. Bitmern Solo charges a flat 1% on finds; you keep 99%. How that is handled and when the payout arrives is covered in 1% fee explained and payout timing. This post does not describe internal payout mechanics.

The extranonce lives here

Your miner changes the nonce in the block header on every attempt. The nonce field is limited, and fast hardware works through it quickly. When it is exhausted, the miner needs a fresh header.

The fix is the extranonce: extra search space inside the coinbase transaction. Changing the extranonce changes the coinbase transaction, which changes the merkle root, which changes the header — giving the miner a fresh nonce range to search.

In stratum terms, the pool sends the coinbase transaction to your miner in two pieces with a gap in the middle. The miner fills the gap with extranonce values. A simplified view, with placeholders only:

EXAMPLE ONLY — simplified coinbase assembly, placeholder values
coinb1      = <C1>            (start of coinbase, from the pool)
extranonce1 = <E1>            (assigned by the pool per connection)
extranonce2 = <E2>            (rolled by your miner)
coinb2      = <C2>            (rest of coinbase, from the pool)
coinbase tx = C1 + E1 + E2 + C2  -> hashed -> combined with merkle branch -> merkle root -> header

You do not configure any of this. Firmware and the pool handle it. The full nonce story is in what is a nonce.

Coinbase maturity: the 100-confirmation rule

New coins from a coinbase transaction cannot be spent straight away. Bitcoin requires coinbase outputs to have 100 confirmations before they can be spent. This is called coinbase maturity.

Why does the rule exist?

1. Blocks can be replaced. Occasionally two miners find a block at about the same time, and only one ends up in the longest chain. The other block — and its coinbase transaction — disappears.
2. New coins have no history. If freshly created coins could be spent immediately and the block was then replaced, those coins and anything built on them would vanish.
3. Maturity removes that risk. Waiting for 100 confirmations makes it extremely unlikely that the block will be replaced.

For a solo miner, this is one reason a find and a spendable payout are not the same moment. Bitmern Solo's specific timing is explained in payout timing.

How to read a coinbase transaction on an explorer

After any find — yours or anyone's — you can inspect the coinbase transaction on a public block explorer:

1. Open the block. Search the block height or block hash.
2. Look at the first transaction. Explorers usually label it "coinbase" and show no normal input address.
3. Read the outputs. These show where the reward went and how much.
4. Compare with subsidy + fees. The explorer typically shows the block's total fees; subsidy plus fees is the most the coinbase can claim.
5. Check confirmations. The count tells you how far the block is from maturity.

For the full step-by-step on confirming your own payout, read verify payout on an explorer.

A worked example of the reward arithmetic (EXAMPLE values only)

The fee figure below is a placeholder to show the arithmetic only. It is not a real block, fee level, or forecast.

EXAMPLE ONLY
Block subsidy (current, since April 2024):  3.125 BTC
Transaction fees in an EXAMPLE block:       F
Block reward:                               3.125 + F
Bitmern Solo flat fee:                      1% × (3.125 + F)
You keep:                                   99% × (3.125 + F)
Spendable after:                            100 confirmations (coinbase maturity)

Replace F with the total fees shown for a real block on an explorer if you want to see what a specific historical block paid.

Ordered "coinbase readiness" checklist

You never build a coinbase transaction yourself, but you can make sure everything around it is right.

1. Confirm your stratum fields

Symptom: You are not sure your miner is on the right endpoint.

Fix: In AxeOS, check the host:

btc.bitmernsolo.com

Port:

3132

Username:

WALLET.worker

Password:

x

Never treat :3102 as the Bitaxe / home default.

2. Verify the wallet behind WALLET.worker

Symptom: You typed the address from memory or copied it a long time ago.

Fix: Check it character by character against your wallet app. An invalid address can cause rejects — see invalid wallet rejects.

3. Make sure you control that wallet

Symptom: The address belongs to an old wallet, a device you no longer have, or an exchange account.

Fix: Use a wallet you hold the keys to and can access long term. To switch safely, follow change payout wallet.

4. Confirm the miner is actually working

Symptom: You want to be sure your shares count.

Fix: Open the matching coin tab on Bitmern Solo and confirm your worker shows fresh accepted shares. That is your miner building headers — including the coinbase it was sent — and searching.

5. Know where a find would show up

Symptom: You are not sure how you would notice a find.

Fix: Read what happens when you find a block so you know what the dashboard and explorer would show.

6. Expect maturity time

Symptom: You are worried a reward would be "missing" right after a find.

Fix: Coinbase outputs need 100 confirmations before they can be spent. Check payout timing for how Bitmern Solo handles timing.

7. Keep expectations honest

Symptom: You are planning around a find.

Fix: Do not. Solo finds are lottery-like, and Current Effort is not a find guarantee — see Current Effort explained. This is not financial advice.

What this post will not invent

• No fee levels, prices, or reward forecasts — no financial advice
• No description of Bitmern Solo internal payout mechanics beyond flat 1% / keep 99% (see the payout and fee posts)
• No claim that :3102 is the home Bitaxe default (easy-start is :3132)

Common coinbase misunderstandings

1. "Coinbase means the exchange." No. The coinbase transaction is a Bitcoin protocol term, unrelated to the company.
2. "The coinbase transaction spends someone's coins." No. It has no real inputs; it creates the reward.
3. "The reward is only the subsidy." It is subsidy plus that block's transaction fees.
4. "A found reward is spendable immediately." Coinbase outputs need 100 confirmations first.
5. "I need to set something in the coinbase." You do not. Your part is a correct WALLET.worker and healthy miner.
6. "High Current Effort means a find is coming." It does not. Current Effort is not a find guarantee.

Soft next step

Open a public block explorer, pick any recent block, and look at its first transaction — that is the coinbase. Then check that the wallet behind your WALLET.worker is valid and yours, and that your worker shows fresh accepted shares on the matching coin tab. Keep BTC easy-start btc.bitmernsolo.com with port :3132 and password x.

Start mining

Start Mining — after login, open the matching coin tab and confirm workers / shares / hashrate.

FAQ

What is a coinbase transaction?

The first transaction in every Bitcoin block. It has no real inputs and creates the block reward: the subsidy plus that block's transaction fees.

Is the coinbase transaction related to Coinbase the exchange?

No. It is a Bitcoin protocol term that is unrelated to the exchange company.

What is coinbase maturity?

The rule that coinbase outputs need 100 confirmations before they can be spent, so a replaced block cannot leave spent coins behind.

What is the block subsidy now?

3.125 BTC per block since the April 2024 halving. See halving explained.

What does Bitmern Solo charge on a find?

A flat 1% — you keep 99%. Details are in 1% fee explained.

Does Current Effort mean I am about to find a block?

No. Current Effort is an ops / attribution signal — not a find guarantee. See Current Effort explained.