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Documentation Index

Fetch the complete documentation index at: https://mintlify.com/mempool/mempool/llms.txt

Use this file to discover all available pages before exploring further.

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Overview

Mempool’s Fee Estimation provides accurate, real-time transaction fee recommendations to help you pay the right amount for the confirmation speed you need. Our algorithms analyze current mempool conditions to predict optimal fees.

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Why Transaction Fees Matter

Bitcoin miners prioritize transactions by fee rate - transactions paying higher fees per byte get confirmed faster. Paying too little means waiting longer; paying too much wastes money.

Save Money

Avoid overpaying by using accurate fee estimates based on current network conditions.

Control Timing

Choose your priority level to balance cost and confirmation time.

Real-Time Data

Fee recommendations update every few seconds based on live mempool data.

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Fee Priority Levels

Mempool provides three priority levels to match your needs:
Next Block (10-20 minutes)Recommended for:
  • Time-sensitive payments
  • Exchange withdrawals
  • Important transactions
  • When network is congested
This fee rate should get your transaction in the next 1-2 blocks.
High priority doesn’t guarantee instant confirmation - block times vary naturally.

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Understanding Fee Rates

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Satoshis per Virtual Byte (sat/vB)

Fees are measured in satoshis per virtual byte:
  • 1 satoshi (sat) = 0.00000001 BTC
  • Virtual byte (vB) = Unit of transaction size (SegWit adjusted)
Total fee = Transaction size × Fee rate Example: 
Transaction size: 250 vB
Fee rate: 20 sat/vB
Total fee: 250 × 20 = 5,000 sats (0.00005 BTC)
SegWit and Taproot transactions are smaller, so you pay less total fees even at the same rate.

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SegWit Discount

SegWit (Segregated Witness) transactions receive a discount on block space:
  • Legacy transactions: 1 byte = 1 vByte
  • SegWit transactions: Witness data counts as 1/4 vByte
  • Result: 30-40% smaller transaction size

Legacy P2PKH

~230 vBytes typicalAt 20 sat/vB = 4,600 sats

SegWit P2WPKH

~140 vBytes typicalAt 20 sat/vB = 2,800 sats (39% savings!)

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How Fee Estimation Works

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Real-Time Analysis

Our fee estimator continuously analyzes:
  1. Current mempool state: Size and composition
  2. Fee rate distribution: What others are paying
  3. Block arrival rate: Recent mining speed
  4. Transaction flow: Incoming transaction rate
  5. Historical patterns: Time-of-day and day-of-week trends

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Estimation Algorithm

The system calculates fee recommendations by:
1

Mempool Sampling

Analyze the current mempool to see which fee rates are represented.
2

Block Projection

Project which transactions would be in the next several blocks based on current conditions.
3

Confirmation Target

Determine the minimum fee rate needed to reach your target confirmation time.
4

Safety Margin

Add a small buffer to account for new incoming transactions.

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Why Estimates Change

Fee recommendations update in real-time as conditions change:
  • Mempool activity: New high-fee transactions arrive
  • Block discovery: New blocks clear out transactions
  • Network events: Market volatility, exchange activity
  • Time patterns: Business hours vs. weekends
Fee estimates are predictions, not guarantees. Unexpected network activity can affect confirmation times.

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Fee Estimation Widget

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Dashboard Display

The fee estimation box shows current recommended rates:
  • Color gradient: Visual indicator from low to high fees
  • Three tiers: No priority, medium, high
  • Sat/vB rates: Current recommended fee rates
  • Live updates: Refreshes every few seconds

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Reading the Display

┌─────────────────────────────────┐
│  Recommended Fees               │
├─────────────────────────────────┤
│  No Priority    │ 5 sat/vB      │
│  Medium Priority│ 12 sat/vB     │
│  High Priority  │ 20 sat/vB     │
└─────────────────────────────────┘
The colored background shows the relative fee range - darker colors indicate higher fees.

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Using Fee Estimates in Wallets

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Manual Entry

When your wallet asks for a fee rate:
  1. Check mempool.space for current recommended rates
  2. Choose your priority level
  3. Enter the sat/vB rate in your wallet
  4. Verify the total fee before confirming
Bookmark mempool.space or keep it open when making transactions.

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API Integration

Wallet developers can integrate our fee API: 
curl "https://mempool.space/api/v1/fees/recommended"

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Wallet-Specific Guidance

Use estimatesmartfee command:
bitcoin-cli estimatesmartfee 6
Or set paytxfee for manual control:
bitcoin-cli settxfee 0.00000020

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Advanced Fee Strategies

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Replace-By-Fee (RBF)

Start with a lower fee and increase if needed:
1

Enable RBF

Set RBF flag when creating transaction (sequence number < 0xfffffffe).
2

Broadcast Low Fee

Send transaction with low priority fee rate.
3

Monitor Position

Watch transaction position in mempool.
4

Bump if Needed

If not confirming fast enough, create replacement with higher fee.
RBF lets you save money by starting low and only paying more if necessary.

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Child-Pays-For-Parent (CPFP)

If you receive a low-fee transaction, speed it up:
  1. Create a new transaction spending the unconfirmed output
  2. Set a high enough fee to cover both transactions
  3. Miners will include both to collect the combined fee

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Weekend Savings

Time your transactions for lower fees:

Expensive Times

  • Monday-Friday business hours
  • Market volatility periods
  • After major news events
  • Exchange activity peaks

Cheap Times

  • Saturday-Sunday
  • Late night hours (UTC)
  • Holiday periods
  • Quiet market conditions

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Fee Calculation Examples

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Simple Payment

Transaction: 1 input, 2 outputs (SegWit)
Size: ~140 vBytes
Fee rate: 15 sat/vB
Total fee: 140 × 15 = 2,100 sats

At $40,000/BTC:
Fee in USD: $0.84

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UTXO Consolidation

Transaction: 10 inputs, 1 output (SegWit)
Size: ~550 vBytes
Fee rate: 5 sat/vB (low priority)
Total fee: 550 × 5 = 2,750 sats

At $40,000/BTC:
Fee in USD: $1.10
Consolidate UTXOs during low-fee periods to save money on future transactions.

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Batched Exchange Withdrawal

Transaction: 2 inputs, 50 outputs (SegWit)
Size: ~1,800 vBytes
Fee rate: 20 sat/vB
Total fee: 1,800 × 20 = 36,000 sats

Cost per recipient: 720 sats
At $40,000/BTC: $0.29 per withdrawal

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Mempool Insights

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Fee Distribution Graph

View how fees are distributed across the mempool:
  • X-axis: Fee rate ranges
  • Y-axis: Amount of transaction data
  • Colors: Different fee tiers
  • Height: Shows concentration at each rate
Analyze fee market evolution:
  • Daily average fees
  • Peak vs. off-peak patterns
  • Seasonal trends
  • Event-driven spikes

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API Reference

Access fee estimation programmatically: 
curl "https://mempool.space/api/v1/fees/recommended"
See API Documentation for complete details.

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Troubleshooting

Check if your fee rate is competitive:
  1. Look up your transaction on mempool.space
  2. Check its position in mempool blocks
  3. Compare your fee rate to current recommendations
  4. Consider RBF or CPFP to speed up
  5. Or use Transaction Acceleration
Fee recommendations reflect current market conditions:
  • Check the mempool size (higher = more expensive)
  • Consider waiting for a quieter period
  • Use low priority if not urgent
  • Check if there’s unusual network activity
No, only when necessary:
  • Most transactions can use medium priority
  • Use high priority for time-sensitive payments
  • Use low priority to save money when possible
  • Monitor the mempool to understand conditions
Different estimation algorithms:
  • Some wallets use outdated data
  • Some add extra margin for safety
  • Some use Bitcoin Core’s estimator
  • Mempool.space uses real-time mempool analysis

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Best Practices

Always check current mempool conditions before sending
Use SegWit or Taproot addresses to save on fees
Enable RBF for flexibility to adjust fees later
Batch multiple payments when possible
Consolidate UTXOs during low-fee periods
Don’t overpay - use appropriate priority level
Consider Lightning Network for small/frequent payments

Mempool Visualizer

See real-time mempool activity and fee distribution

Transaction Acceleration

Speed up stuck transactions with low fees

Blockchain Explorer

Look up transaction details and confirmation status

Lightning Explorer

Explore Lightning Network for instant, low-fee payments

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