BEGINNER_DOC_017 // BEGINNERS / SENDING
SENDING
BITCOIN
BITCOIN
Sending bitcoin means constructing a transaction that spends your UTXOs and creates new outputs
locked to the recipient's address. The process is irreversible — once confirmed,
a transaction cannot be undone. Always verify the recipient address, fee rate, and amount
before broadcasting.
HOW_A_SEND_WORKS_STEP_BY_STEP
WHAT YOUR WALLET DOES BEHIND THE SCENES
1. UTXO Selection
Wallet scans your UTXOs, selects enough to cover amount + fee
Strategy: minimize inputs (fewer = smaller tx = lower fee)
2. Transaction Construction
Inputs: reference selected UTXOs (TxID + Vout)
Outputs: [recipient address + amount] + [change address + change]
Fee: inputs total − outputs total = miner fee
3. Signing
Wallet signs each input with the corresponding private key
Signature proves ownership without revealing the key
4. Broadcast
Signed transaction sent to Bitcoin nodes via P2P network
Nodes validate and add to mempool
5. Confirmation
Miner includes tx in a block → first confirmation
Each new block = one more confirmation
TRANSACTION_FEES
Fee Rate — sat/vbyte
FEE MARKET
Fees are set as a rate per virtual byte of transaction size. Higher fee rate = higher priority
in the mempool = faster confirmation. The market price of block-space/">block space is set by supply and demand.
Fee calculation:
fee = vsize × fee_rate
Example: 1-in 2-out P2WPKH transaction
vsize: ~141 vbytes
fee rate: 20 sat/vbyte (moderate priority)
fee total: 141 × 20 = 2,820 satoshis = ~$2.80 @ $100k BTC
Typical fee ranges (2024, varies widely):
Low priority (>1 hour): 1–5 sat/vbyte
Normal (~10 min): 10–30 sat/vbyte
High priority (~1 block): 50–200+ sat/vbyte
Fees spike during periods of high demand. Check mempool.space for current fee estimates before sending.
Change Outputs
UTXO MODEL
UTXOs must be spent entirely. If you spend a 0.5 BTC UTXO to send 0.3 BTC, the remaining
0.2 BTC (minus fee) is sent back to a change address in your own wallet.
You have: 1 UTXO of 0.50000000 BTC
You send: 0.30000000 BTC to Alice
Transaction:
Input: 0.50000000 BTC (your UTXO — fully consumed)
Output1: 0.30000000 BTC (to Alice)
Output2: 0.19997180 BTC (change back to you)
Fee: 0.00002820 BTC (141 vbytes × 20 sat/vbyte)
Your wallet creates a fresh address for the change output.
Change addresses are important for privacy. Reusing the same change address links all your transactions together on-chain.
⚠ BEFORE YOU SEND — CRITICAL CHECKS
Verify the address. Always double-check the first and last 4 characters of the recipient address. Clipboard malware can silently replace addresses.
Transactions are irreversible. No bank, no Anthropic, no developer can reverse a confirmed Bitcoin transaction. There is no fraud department.
Set an appropriate fee. Too low and your transaction may be stuck in the mempool for hours or days. Use RBF if supported by your wallet.
Transactions are irreversible. No bank, no Anthropic, no developer can reverse a confirmed Bitcoin transaction. There is no fraud department.
Set an appropriate fee. Too low and your transaction may be stuck in the mempool for hours or days. Use RBF if supported by your wallet.
TERMINOLOGY_INDEX
sat/vbyte
Satoshis per virtual byte. The unit used to set transaction fee rates.
Change Address
An address in your own wallet that receives leftover funds after a UTXO is spent.
Mempool
The pool of unconfirmed transactions waiting to be included in a block. Higher fees = priority.
RBF
Replace-By-Fee. A mechanism to replace an unconfirmed transaction with one that pays a higher fee.
CPFP
Child-Pays-For-Parent. Spending an unconfirmed output with a high-fee child transaction to speed up confirmation.
Confirmation
Each block mined on top of the block containing your transaction adds one confirmation. 6+ is standard for finality.