Best Practices After CoinJoin

Mixing your coins is only half the battle. How you handle and spend mixed coins determines whether you maintain privacy or accidentally undo all your work.

The Golden Rules

Critical Rules — Never Break These

1. Never merge mixed coins with KYC/unmixed coins
2. Never send multiple mixed UTXOs to the same address
3. Always use your own node
4. Use coin control for every transaction

Rule 1: Never Merge Mixed and Unmixed Coins

This is the most common mistake that destroys CoinJoin privacy.

What Merging Looks Like

BAD TRANSACTION:
─────────────────────────────────────────────────
INPUTS                          OUTPUT
──────                          ──────
0.1 BTC (mixed, private)   ─┬─→ 0.25 BTC (payment)
0.15 BTC (KYC, not mixed)  ─┘

Result: The mixed coin is now linked to your identity!

When you combine a mixed UTXO with an unmixed one:

• The unmixed coin is linked to your identity (from the exchange)
• Both coins are now in the same transaction
• The mixed coin is now also linked to your identity
• All mixing effort wasted

How to Avoid This

Use separate wallets:

Wallet 1: "Exchange/KYC Wallet"
  └─ Contains coins from exchanges
  └─ Never mixed
  └─ For regulated activities

Wallet 2: "Private Wallet"  
  └─ Contains only mixed coins
  └─ Connect to your own node
  └─ For private spending

Or use careful labeling:

• Label every UTXO as "mixed" or "unmixed"
• Never let them touch each other

Rule 2: Don't Consolidate Mixed Coins

Sending multiple mixed UTXOs to the same address reveals they belong to the same person.

The Problem

BAD TRANSACTION:
─────────────────────────────────────────────────
INPUTS                          OUTPUT
──────                          ──────
0.1 BTC (mixed, round 1)   ─┬─→ 0.3 BTC (your address)
0.1 BTC (mixed, round 2)   ─┤
0.1 BTC (mixed, round 3)   ─┘

Observer: "These three mixed coins belong to the same person!"

Before this transaction, each 0.1 BTC could have belonged to anyone. After consolidating, it's clear they all belong to you.

Better Approach

Spend mixed coins individually when possible:

GOOD: Individual Spends
─────────────────────────────────────────────────
Tx 1: 0.1 BTC (mixed) → Payment
Tx 2: 0.1 BTC (mixed) → Different payment
Tx 3: 0.1 BTC (mixed) → Another payment

If you must combine (for a larger payment), understand you're trading privacy for utility.

Rule 3: Handle Change Carefully

When you spend a mixed coin, you may receive change. This change has reduced privacy.

Example

Spending mixed coin:
─────────────────────────────────────────────────
INPUT                           OUTPUTS
─────                           ───────
0.1 BTC (mixed, private)   →    0.05 BTC (payment)
                                0.049 BTC (change back to you)

The 0.049 BTC change is now:

• Obviously linked to whoever made the payment
• Less private than the original mixed coin
• Should be considered "semi-tainted"

Options for Change

1. Remix it — Send it through CoinJoin again
2. Use it for non-private spending — Since it's already somewhat exposed
3. Combine it with other change — Not with fresh mixed coins
4. Spend it entirely — No change if amount matches exactly (rare)

Ideal: Avoid Change Entirely

When possible, select UTXOs that match your payment closely:

Payment needed: 0.099 BTC
Your mixed UTXOs: 0.1 BTC, 0.05 BTC, 0.02 BTC

Best choice: Use the 0.1 BTC (leaves only 0.001 BTC change)
Worst choice: Use 0.05 + 0.05 + 0.02 BTC (consolidates AND creates change)

Rule 4: Always Use Your Own Node

This applies to all Bitcoin usage, but is critical for mixed coins.

Why It Matters

When your wallet connects to a node:

• It requests information about your addresses
• It reveals your IP address
• The node operator learns which addresses belong to you

If you use someone else's node (or a random public node):

• A surveillance company might run that node
• They learn all your addresses, including mixed ones
• Your privacy is compromised

Solution

Run your own Bitcoin node. When you query your own node:

• You're asking yourself about your addresses
• No third party learns anything
• True privacy

See our Bitcoin Node guide to set up your own.

Rule 5: Use Coin Control

Coin control is the ability to choose exactly which UTXOs you spend.

Without Coin Control

Your wallet automatically selects coins:

• It might grab a mixed coin and an unmixed coin
• It might consolidate multiple UTXOs unnecessarily
• You lose control of your privacy

With Coin Control

You explicitly choose:

• "I want to spend THIS specific 0.1 BTC UTXO"
• "I do NOT want to include any other coins"

Wallets with Good Coin Control

• Sparrow Wallet — Excellent coin control, labeling, and visualization
• Electrum — Good coin control (Coins tab)
• Wasabi — Decent coin control

How to Use Coin Control

In Sparrow:

1. Go to UTXOs tab
2. Right-click the specific UTXO you want to spend
3. Select Send Selected
4. This ensures ONLY that UTXO is used

In Electrum:

1. Go to Coins tab (View → Show Coins)
2. Right-click the UTXO
3. Select Spend From

Rule 6: Consider Lightning Network

Opening Lightning channels with mixed coins adds another privacy layer.

How It Helps

Mixed coins → Open Lightning channel → Make Lightning payments

• The channel opening is on-chain (visible)
• But Lightning payments are NOT on the public blockchain
• Recipients see a Lightning payment, not on-chain history
• When you close the channel, the link to original mix is further obscured

Best Practice

1. Mix your coins (CoinJoin)
2. Open Lightning channels with mixed UTXOs
3. Spend via Lightning for everyday purchases
4. Close channels eventually (coins have new history)

Rule 7: Be Patient

Don't spend mixed coins immediately after mixing.

Why Timing Matters

If you:

1. CoinJoin at 2:00 PM
2. Spend from a mixed output at 2:15 PM

An observer might correlate the timing:

• "One of the CoinJoin outputs was spent 15 minutes later"
• "Let's see which participant was likely to spend quickly"

Better Practice

• Let mixed coins "age" for hours, days, or weeks
• Don't be the first or last to move coins after a mix
• Blend into normal usage patterns

Checklist: Before Spending Mixed Coins

Before making a transaction with mixed coins, ask yourself:

• Am I using my own node?
• Am I using coin control to select specific UTXOs?
• Are ALL inputs in this transaction from my mixed pool?
• Am I NOT combining multiple mixed UTXOs unnecessarily?
• Is the change amount acceptable? (or can I adjust to minimize it?)
• Has enough time passed since the mix?

Common Mistakes Summary

Mistake	Why It's Bad	How to Avoid
Merging mixed + unmixed	Links mixed coins to your identity	Separate wallets
Consolidating mixed UTXOs	Reveals common ownership	Spend individually
Using public node	Node learns your addresses	Run your own node
No coin control	Wallet makes poor choices	Use Sparrow/Electrum
Spending immediately	Timing analysis possible	Wait before spending
Ignoring change	Change has reduced privacy	Remix or handle carefully

Summary

CoinJoin gives you privacy, but only if you maintain it:

1. Separate mixed from unmixed — Never let them touch
2. Spend mixed coins individually — Don't consolidate
3. Use your own node — Essential for real privacy
4. Use coin control — Be deliberate about what you spend
5. Be patient — Don't rush to spend after mixing

Privacy is a practice, not a one-time action. Every transaction is an opportunity to preserve or destroy your privacy.

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Related Guides:

• UTXO Management — Master coin control and consolidation
• Coin Control Guide — Detailed coin control techniques
• Bitcoin Node Setup — Run your own node
• Understanding Transactions — Know how transactions work