BA-00P · LESSON 03

Send with fee and change

KEY DEFINITIONS

Terms used in this lesson

Transaction ID: The identifier produced by hashing a Bitcoin transaction’s non-witness serialization.

Review destination, amount, selected outputs, fee rate, absolute fee, and change before signing a simulated Bitcoin payment.

55 min Difficulty 1/5 Not started

VISUAL MODEL

See the whole mechanism before going step by step

Use the diagrams to orient yourself. Then the guided explanation below teaches every part in depth.

4 explanatory views

CONCEPT-SPECIFIC MAP · send paymentBuild a payment that balances before signingSelect any state to inspect its exact role.

RELATIONSHIP MAPInputs, rule, and outputs

01
SELECT70k + 45k sats
Bitcoin consumes complete previous outputs, not fractions of an account balance.
02
PAY80,000 sats to Bob
The wallet must verify the destination before authorizing the transaction.
03
FEE1,200 sats
The fee is the difference between total inputs and total outputs.
04
CHANGE33,800 sats
Change is a new output back to the sender's wallet.
05
SIGNAuthorize exact transaction
The signing display is the last reliable place to catch destination substitution.

Rule shown: Selected inputs must exactly equal payment outputs plus change outputs plus fee.

STAGE 1 OF 5SELECT: 70k + 45k sats

Bitcoin consumes complete previous outputs, not fractions of an account balance.

Governing relationship: Selected inputs must exactly equal payment outputs plus change outputs plus fee. Complete path: 1. SELECT, 70k + 45k sats. Bitcoin consumes complete previous outputs, not fractions of an account balance. 2. PAY, 80,000 sats to Bob. The wallet must verify the destination before authorizing the transaction. 3. FEE, 1,200 sats. The fee is the difference between total inputs and total outputs. 4. CHANGE, 33,800 sats. Change is a new output back to the sender's wallet. 5. SIGN, Authorize exact transaction. The signing display is the last reliable place to catch destination substitution.

1. State transitionWhat exists, what changes, and what results

BEFORE

The wallet selects outputs worth 70,000 and 45,000 sats, pays 80,000 sats, and estimates a 1,200 sat fee.

MECHANISM

Confirm the Bitcoin network, compare the address using an independent channel for high-value payments, and state the amount in both sats and any local-currency estimate witho…

AFTER

A safe send combines value conservation with human verification of the exact transaction before signing.

Text equivalent: Starting from The wallet selects outputs worth 70,000 and 45,000 sats, pays 80,000 sats, and estimates a 1,200 sat fee. The mechanism begins when Confirm the Bitcoin network, compare the address using an independent channel for high-value payments, and state the amount in both sats and any local-currency estimate without confusing the estimate for protocol value. The resulting lesson is A safe send combines value conservation with human verification of the exact transaction before signing.

2. Mechanism pathSelect a stage to inspect its job

STAGE 1 OF 5

Verify destination and amount

Confirm the Bitcoin network, compare the address using an independent channel for high-value payments, and state the amount in both sats and any local-currency estimate without confusing the estimate for protocol value.

Complete path: 1. Verify destination and amount: Confirm the Bitcoin network, compare the address using an independent channel for high-value payments, and state the amount in both sats and any local-currency estimate without confusing the estimate for protocol value. 2. Inspect selected inputs: Coin selection affects fee, privacy, and change. Spending an output consumes it entirely even when the payment uses only part of its value. 3. Calculate outputs and fee: The wallet creates the recipient output, a new change output when economical, and a fee equal to total inputs minus total outputs. 4. Review before signing: Use the signing device's trusted display when available. Check destination, amount, fee, and change rather than approving a vague request from the online computer. 5. Broadcast and monitor: After signing, the wallet broadcasts the transaction. Monitor txid, replacement state, and confirmations without assuming broadcast guarantees inclusion.

3. Rule and failure boundaryWhat accepts the result and where it can stop

ACCEPTED PATH

Input values must cover every output plus the fee, each input must be available and authorized, and the signed transaction must match the reviewed transaction.

CHANGED CONDITION

If malware replaces the destination before signing, only a trusted-display comparison can reveal it. If the signer authorizes the changed output, Bitcoin will enforce that mistaken authorization.

Important distinction: The wallet sends part of an existing coin and leaves the rest inside it. Bitcoin spends whole outputs. Any remaining value must be created as an entirely new change output.

Text equivalent: The accepted path is enforced by Input values must cover every output plus the fee, each input must be available and authorized, and the signed transaction must match the reviewed transaction. If the required condition changes, If malware replaces the destination before signing, only a trusted-display comparison can reveal it. If the signer authorizes the changed output, Bitcoin will enforce that mistaken authorization.

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Learn the idea

Sending bitcoin is a complete state transition. A wallet selects existing outputs, creates the recipient output and usually a change output, estimates a fee from transaction size and fee rate, then asks the signer to authorize exact transaction data. The fee is inputs minus outputs, not a separate network invoice.

GUIDED EXPLANATION1/5 ideas inspected

Verify destination and amount

The worked example follows the explanation

Inspect every idea above to open it.

Important distinction“The wallet sends part of an existing coin and leaves the rest inside it.”

Bitcoin spends whole outputs. Any remaining value must be created as an entirely new change output.

FINISH LEARNING FIRST

The questions unlock after every required learning activity

Inspect every guided idea, open the worked example, rebuild its mechanism, and complete the deterministic lesson tool. Your progress is saved automatically.