Bitcoin (BTC), the pioneering cryptocurrency launched in 2009, operates on a meticulously engineered protocol that balances scarcity, security, and scalability. This post dissects key technical parameters: the fixed 21 million BTC supply cap, indefinite block production (~6.9 million until subsidy exhaustion), transaction capacity per block (~2,500-3,500 average), and the computational intensity of mining (network target: 10 minutes per block via ~631 sextillion hashes). These elements ensure decentralized consensus while mitigating inflation and spam.
Data reflects status as of November 08, 2025 (block height ~919,800; ~19.75 million BTC mined, 94% of cap). We include a comprehensive halving schedule table for reward progression.
Total Supply: The 21 Million Cap
Bitcoin’s supply is hard-capped at 21 million BTC, an intentional design to emulate scarce assets like gold and prevent inflationary debasement. New coins are issued exclusively through block rewards, which halve every 210,000 blocks (~4 years), creating a geometric series that converges to the limit by ~2140.
- Issuance Mechanism: Rewards start at 50 BTC/block (2009); Current: 3.125 BTC/block (post-2024 halving).
- Circulating Supply: ~19.75 million BTC (94%); Remaining ~1.25 million to mine.
- Post-Cap Sustainability: After subsidies end, miners earn transaction fees (~$5 million daily in 2025, ~20% of revenue).
- Economic Impact: Fixed supply drives scarcity; Historical halvings correlate with 4x average price surges.
Bitcoin Halving Schedule: Reward Evolution and Supply Distribution
Bitcoin’s block reward halves approximately every 4 years (every 210,000 blocks, or ~1,314 days at 10-minute intervals), starting from 50 BTC per block in 2009. This creates 34 halving eras (0-33), after which rewards reach effectively zero (~2140), and miners rely solely on transaction fees. The total supply caps at 21 million BTC, with ~19.75 million mined as of November 8, 2025 (94% complete).
The table below outlines all eras, including approximate years (based on historical averages; actual dates vary slightly due to difficulty adjustments), blocks mined in the era, reward per block, new coins issued, cumulative supply, and percentage of the cap. Eras are numbered from 0 (genesis).
| Era | Approximate Years | Blocks in Era | Reward per Block (BTC) | New Coins per Era (BTC) | Cumulative Supply (BTC) | % of 21M Cap |
|---|---|---|---|---|---|---|
| 0 | 2009–2012 | 210,000 | 50 | 10,500,000 | 10,500,000 | 50.00% |
| 1 | 2012–2016 | 210,000 | 25 | 5,250,000 | 15,750,000 | 75.00% |
| 2 | 2016–2020 | 210,000 | 12.5 | 2,625,000 | 18,375,000 | 87.50% |
| 3 | 2020–2024 | 210,000 | 6.25 | 1,312,500 | 19,687,500 | 93.75% |
| 4 | 2024–2028 | 210,000 | 3.125 | 656,250 | 20,343,750 | 96.88% |
| 5 | 2028–2032 | 210,000 | 1.5625 | 328,125 | 20,671,875 | 98.44% |
| 6 | 2032–2036 | 210,000 | 0.78125 | 164,062.5 | 20,835,937.5 | 99.22% |
| 7 | 2036–2040 | 210,000 | 0.390625 | 82,031.25 | 20,917,968.75 | 99.61% |
| 8 | 2040–2044 | 210,000 | 0.1953125 | 41,015.625 | 20,958,984.375 | 99.80% |
| 9 | 2044–2048 | 210,000 | 0.09765625 | 20,507.8125 | 20,979,492.1875 | 99.90% |
| 10 | 2048–2052 | 210,000 | 0.048828125 | 10,253.90625 | 20,989,746.09375 | 99.95% |
| 11 | 2052–2056 | 210,000 | 0.0244140625 | 5,126.953125 | 20,994,873.046875 | 99.98% |
| 12 | 2056–2060 | 210,000 | 0.01220703125 | 2,563.4765625 | 20,997,436.5234375 | 99.99% |
| 13 | 2060–2064 | 210,000 | 0.006103515625 | 1,281.73828125 | 20,998,718.26171875 | 99.99% |
| 14 | 2064–2068 | 210,000 | 0.0030517578125 | 640.869140625 | 20,999,359.130859375 | 100.00% |
| 15 | 2068–2072 | 210,000 | 0.00152587890625 | 320.4345703125 | 20,999,679.565429688 | 100.00% |
| 16 | 2072–2076 | 210,000 | 0.000762939453125 | 160.21728515625 | 20,999,839.782714844 | 100.00% |
| 17 | 2076–2080 | 210,000 | 0.0003814697265625 | 80.108642578125 | 20,999,919.891357422 | 100.00% |
| 18 | 2080–2084 | 210,000 | 0.00019073486328125 | 40.0543212890625 | 20,999,959.945678711 | 100.00% |
| 19 | 2084–2088 | 210,000 | 0.000095367431640625 | 20.02716064453125 | 20,999,979.972839355 | 100.00% |
| 20 | 2088–2092 | 210,000 | 0.0000476837158203125 | 10.013580322265625 | 20,999,989.986419678 | 100.00% |
| 21 | 2092–2096 | 210,000 | 0.00002381185791015625 | 5.0067901611328125 | 20,999,994.993209839 | 100.00% |
| 22 | 2096–2100 | 210,000 | 0.000011905928955078125 | 2.5033950805664062 | 20,999,997.49660492 | 100.00% |
| 23 | 2100–2104 | 210,000 | 0.0000059529644775390625 | 1.2516975402832031 | 20,999,998.74830246 | 100.00% |
| 24 | 2104–2108 | 210,000 | 0.0000029764822387695312 | 0.6258487701416016 | 20,999,999.37415123 | 100.00% |
| 25 | 2108–2112 | 210,000 | 0.0000014882411193847656 | 0.3129243850708008 | 20,999,999.687075615 | 100.00% |
| 26 | 2112–2116 | 210,000 | 0.0000007441205596923828 | 0.1564621925354004 | 20,999,999.843537807 | 100.00% |
| 27 | 2116–2120 | 210,000 | 0.0000003720602798461914 | 0.0782310962677002 | 20,999,999.921768903 | 100.00% |
| 28 | 2120–2124 | 210,000 | 0.0000001860301399230957 | 0.0391155481338501 | 20,999,999.960884451 | 100.00% |
| 29 | 2124–2128 | 210,000 | 0.00000009301506996154785 | 0.01955777406692505 | 20,999,999.9804422255 | 100.00% |
| 30 | 2128–2132 | 210,000 | 0.000000046507534980773926 | 0.009778887033462525 | 20,999,999.9902211123 | 100.00% |
| 31 | 2132–2136 | 210,000 | 0.000000023253767490386963 | 0.0048894435167312625 | 20,999,999.9951105564 | 100.00% |
| 32 | 2136–2140 | 210,000 | 0.000000011626883745193481 | 0.002444721758365631 | 20,999,999.997555278 | 100.00% |
| 33 | 2140+ | Infinite | ~0 | ~0 | 21,000,000 |
Block Production: Indefinite but Predictable
Blocks are the backbone of Bitcoin’s ledger, produced approximately every 10 minutes through Proof-of-Work (PoW) mining. There is no fixed number of blocks—the chain grows indefinitely to record transactions, but subsidies end after ~6.9 million blocks.
- Block Interval: Target 10 minutes, adjusted every 2,016 blocks (~2 weeks) to maintain consistency despite varying hash rate.
- Total Blocks to Subsidy End: ~6.9 million (from genesis block 0 in 2009 to ~2140).
- Blocks Mined to Date: ~919,800 (~16 years of ~144 blocks/day).
- Chain Size: ~500 GB full (headers + txns); Pruned nodes ~5 GB (UTXOs only).
- Purpose: Each block bundles txns, timestamps state, and links via prev_hash for immutability.
Growth is linear with txn volume, not block count—E.g., SegWit (2017) increased capacity 4x without more blocks.
Transaction Capacity per Block: Efficiency in Batches
Blocks are not single-txn units; they batch multiple transactions to optimize PoW cost and network resources. Average capacity is 2,500-3,500 txns/block, but varies with size and fee pressure.
- Block Size Limit: 1 MB raw (pre-SegWit); ~4 MB effective with SegWit (separates signatures for 75% space savings).
- Txn Size: Simple ~200 bytes; Complex (e.g., Ordinals) ~1 KB.
- Average Txns/Block: 2,500 (2025); Peak ~4,000 during congestion.
- Daily Capacity: ~350,000-500,000 txns (~144 blocks/day).
- If 1 Txn/Block: Wasteful (~$20 PoW cost for 80-byte header overhead); Fees encourage packing (average fee ~10 sat/byte).
| Block Metric | Value (2025 Average) | Historical Peak (2021) | Efficiency Note |
|---|---|---|---|
| Size | 1.5-2 MB | 3.9 MB | SegWit enables more txns without expansion. |
| Txns per Block | 2,500-3,500 | ~4,000 | Fees prioritize high-value txns first. |
| Daily Txns | ~400,000 | ~1.3 million | Layer 2 (Lightning) offloads ~50%. |
| If 1 Txn Only | Rare (~1%) | N/A | Wastes ~99% capacity; Discouraged by economics. |
Mining Hash Computation: The 10-Minute Puzzle
Mining requires guessing a nonce such that the block hash starts with sufficient zeros (difficulty target). The network targets 10 minutes/block, but this is probabilistic—average ~631 sextillion hashes per block in 2025.
- Hash Function: Double SHA-256 on block header (80 bytes).
- Difficulty: ~147 trillion (2025); Adjusts to keep 10-min average.
- Guesses per Block: ~6.31 × 10^23 (631 sextillion); Network hash rate ~650 EH/s (~10^21 hashes/s) achieves it in 10 min.
- Solo Mining Time: Infeasible (~50 billion years on a GPU); Pools share work for ~minutes payouts.
- Why 10 Min?: Balances security (propagation time ~10s globally) and usability (not too slow for txns).
| Mining Metric | Value (2025) | Historical (2010) | Impact |
|---|---|---|---|
| Difficulty | 147 trillion | 14,000 | Higher = More guesses needed; Adjusts ~2 weeks. |
| Hashes per Block | 631 sextillion | ~4.3 billion | Network solves in 10 min; Solo: Eons. |
| Block Time | 10 min average | Same (target) | Propagation + security threshold. |
| Energy Cost | ~$20/block | ~$0.01 | Fees (~0.5 BTC) cover ~20% revenue. |
Implications for Custom Blockchain Design
For your project:
- Supply: 21M cap via halving (utils.py configurable).
- Blocks: Indefinite; Set 10-min target for stability.
- Txns/Block: Default no limit; Add 1KB limit for efficiency.
- Mining: PoW with adjustable difficulty; Test solo in main.py.