BMMAA Pool Concentration Risk
BMM analyses the periodic new Addition and Attrition of hashrate flowing through the network from the position of top pool concentration risk, as a live indication of the network's decentralisation direction.
(top 5 absorbing hashrate from smaller pools; plausibly large operators adding capacity at, or moving to, the biggest pools)
Last 30 days vs previous 30, to 18 Oct 2026: top 5 +63 EH/s (+8.9%), other pools -14 EH/s (-6.6%); top 5 79.6% of blocks.
What it shows
Pools decide how most Bitcoin blocks are built, and the 5 largest pools find about 4 blocks in 5. BMMAA compares how fast the hashrate behind the top 5 pools grows or shrinks with how fast it grows or shrinks at all other pools. The answer is a single number from −1 to +1. Around zero the network is developing pro rata: hashrate is added or removed on both sides in proportion. Above zero the largest pools are absorbing hashrate and concentration risk is rising; below zero smaller pools are gaining and the pool ecosystem is decentralising. BMM publishes it daily to make that direction visible, with the aim of seeing it at zero or below.
How it is calculated
Every day BMM counts the blocks found by each pool on its own Bitcoin node and converts the shares into hashrate with the node's network estimate. Single days carry too much random block luck, so BMMAA compares the last 30 full UTC days with the previous 30:
gT = change in top 5 hashrate ÷ top 5 hashrate before
gO = change in other pools' hashrate ÷ their hashrate before
BMMAA = (gT − gO) ÷ (|gT| + |gO| + 10%)
The 10% term is a block-luck allowance: it keeps small moves close to zero instead of letting them swing to ±1. The same formula is applied epoch by epoch in the BMM Mining Pools Review.
The scale
| BMMAA | Signal | What it means (plausible reading) |
|---|---|---|
| above +0.60 | Red alert · strong concentration | (top 5 absorbing hashrate from smaller pools; plausibly large operators adding capacity at, or moving to, the biggest pools) |
| +0.30 to +0.60 | Amber · concentrating | (top 5 growing clearly faster than smaller pools) |
| −0.30 to +0.30 | Neutral · organic / pro rata | (within the range block luck alone produces; no clear shift between large and small pools) |
| −0.60 to −0.30 | Blue · decentralising | (smaller pools growing clearly faster than the top 5) |
| below −0.60 | Deep blue · strong decentralisation | (hashrate moving away from the top 5; plausibly miners redirecting to smaller pools) |
In practice
Real epochs from BMM's data. The EH/s columns show the size of each move; BMMAA shows its direction.
| Epoch from | Network EH/s | Network Δ EH/s | Top 5 Δ EH/s | Other pools Δ EH/s | Top 5 growth | Other pools growth | BMMAA | Signal |
|---|---|---|---|---|---|---|---|---|
| 7 Feb 2026 | 1,012 | +88 | +86 | +2 | +12.1% | +1.1% | +0.47 | Amber |
| 27 Jun 2026 | 951 | +17 | +37 | -19 | +5.2% | -8.8% | +0.58 | Amber |
| 11 Jul 2026 | 897 | -54 | -38 | -16 | -5.1% | -7.9% | +0.12 | Neutral |
| 23 Aug 2026 | 902 | -8 | -27 | +19 | -3.8% | +9.5% | -0.57 | Blue |
| 19 Sep 2026 | 944 | +0 | +16 | -16 | +2.2% | -7.4% | +0.49 | Amber |
| 3 Oct 2026 | 990 | +46 | +44 | +2 | +5.8% | +1.0% | +0.28 | Neutral |
Change against the previous epoch; EH/s = share of blocks × epoch-average network hashrate (BMM node). Network = top 5 + other pools.
The epoch from 27 June is a clear case of absorption: the network added hashrate, but the top 5 added more than all of it while other pools shrank. In the epoch from 23 August the network fell, yet smaller pools grew: hashrate moved away from the largest pools. In early July (epoch from 11 July) the top 5 and other pools both fell by similar proportions during Texas grid curtailment, so BMMAA stayed near neutral.
History
Bars: BMMAA per difficulty epoch. Dashed line: the daily 30-day value. Background: the five zones.
All epochs since September 2025
| Epoch from | Block | Retarget | Network EH/s | Top 5 share | Top 5 EH/s | Top 3 share | Top 3 EH/s | Top 5 Δ EH/s | Other Δ EH/s | BMMAA | Signal |
|---|---|---|---|---|---|---|---|---|---|---|---|
| 1 Oct 2025 | 917,280 | +5.97% | 1,038 | 79.4% | 825 | 59.4% | 617 | -5 | -14 | +0.33 | Amber |
| 16 Oct 2025 | 919,296 | -2.73% | 1,119 | 78.0% | 873 | 58.4% | 653 | +48 | +33 | -0.30 | Blue |
| 29 Oct 2025 | 921,312 | +6.31% | 1,098 | 78.2% | 859 | 57.9% | 636 | -14 | -7 | +0.08 | Neutral |
| 12 Nov 2025 | 923,328 | -2.37% | 1,073 | 78.5% | 843 | 60.0% | 644 | -16 | -9 | +0.11 | Neutral |
| 27 Nov 2025 | 925,344 | -1.95% | 1,057 | 78.0% | 825 | 58.1% | 614 | -18 | +2 | -0.22 | Neutral |
| 11 Dec 2025 | 927,360 | -0.74% | 1,060 | 77.2% | 818 | 57.3% | 607 | -7 | +9 | -0.32 | Blue |
| 25 Dec 2025 | 929,376 | +0.04% | 1,061 | 77.4% | 822 | 59.8% | 635 | +4 | -2 | +0.13 | Neutral |
| 8 Jan 2026 | 931,392 | -1.20% | 1,014 | 76.1% | 772 | 58.2% | 591 | -49 | +3 | -0.41 | Blue |
| 22 Jan 2026 | 933,408 | -3.28% | 924 | 76.9% | 711 | 56.7% | 524 | -62 | -28 | +0.13 | Neutral |
| 7 Feb 2026 | 935,424 | -11.16% | 1,012 | 78.7% | 797 | 58.1% | 588 | +86 | +2 | +0.47 | Amber |
| 19 Feb 2026 | 937,440 | +14.73% | 1,046 | 76.9% | 805 | 58.3% | 610 | +8 | +26 | -0.48 | Blue |
| 5 Mar 2026 | 939,456 | +0.45% | 985 | 77.1% | 759 | 60.4% | 595 | -45 | -16 | +0.05 | Neutral |
| 20 Mar 2026 | 941,472 | -7.76% | 987 | 78.8% | 777 | 60.3% | 595 | +18 | -16 | +0.49 | Amber |
| 3 Apr 2026 | 943,488 | +3.87% | 962 | 76.3% | 734 | 60.6% | 583 | -43 | +19 | -0.59 | Blue |
| 17 Apr 2026 | 945,504 | -2.43% | 960 | 77.6% | 745 | 58.3% | 560 | +11 | -13 | +0.41 | Amber |
| 2 May 2026 | 947,520 | -2.30% | 974 | 77.5% | 755 | 58.1% | 566 | +10 | +4 | -0.04 | Neutral |
| 15 May 2026 | 949,536 | +3.12% | 981 | 78.2% | 767 | 59.6% | 585 | +13 | -6 | +0.30 | Amber |
| 29 May 2026 | 951,552 | +1.72% | 929 | 76.5% | 711 | 56.5% | 525 | -57 | +5 | -0.49 | Blue |
| 14 Jun 2026 | 953,568 | -10.09% | 934 | 76.3% | 712 | 56.3% | 526 | +1 | +3 | -0.10 | Neutral |
| 27 Jun 2026 | 955,584 | +7.15% | 951 | 78.8% | 749 | 57.7% | 549 | +37 | -19 | +0.58 | Amber |
| 11 Jul 2026 | 957,600 | -5.00% | 897 | 79.3% | 711 | 62.8% | 563 | -38 | -16 | +0.12 | Neutral |
| 25 Jul 2026 | 959,616 | -0.74% | 903 | 77.9% | 703 | 60.3% | 545 | -8 | +14 | -0.46 | Blue |
| 8 Aug 2026 | 961,632 | +0.99% | 910 | 78.4% | 713 | 59.9% | 545 | +10 | -3 | +0.23 | Neutral |
| 23 Aug 2026 | 963,648 | -1.31% | 902 | 76.1% | 686 | 58.1% | 523 | -27 | +19 | -0.57 | Blue |
| 5 Sep 2026 | 965,664 | +1.31% | 943 | 77.8% | 734 | 59.1% | 558 | +47 | -6 | +0.49 | Amber |
| 19 Sep 2026 | 967,680 | +4.16% | 944 | 79.4% | 750 | 61.9% | 584 | +16 | -16 | +0.49 | Amber |
| 3 Oct 2026 | 969,696 | -0.03% | 990 | 80.2% | 794 | 63.8% | 631 | +44 | +2 | +0.28 | Neutral |
Block luck and limits
Which pool finds the next block is random. Even with nothing changing, luck alone moves BMMAA by about ±0.36 between two epochs and ±0.30 between two 30-day windows (BMM simulation with the top 5 at 78% of blocks). That is why the neutral zone is ±0.30, and why a reading beyond ±0.60 (about twice the luck range) is treated as an alert: luck alone gets there only about 1 time in 20. Block attribution shows where blocks were found, not which miners connected where; pools that do not tag their blocks count as "other pools"; and the EH/s figures are estimates from block counts. BMM also keeps in view the potential issue of hashrate linked to a Block Withholding Attack (BWH).
The top 5
The top 5 are Foundry USA, AntPool, F2Pool, ViaBTC and SpiderPool: the 5 largest pools by blocks on BMM's node at the 29 May 2026 baseline. The set is kept fixed so the series stays comparable, and is reviewed with each Mining Pools Review. Note: in the data from 12–18 October 2026 SpiderPool's share fell sharply and it is no longer among the 5 largest pools on recent days; it is still included in all figures on this page. BMM will update the set in the next review.
How to cite
BMMAA Pool Concentration Risk, BTC Mining Markets (btcmining.markets/insights/bmmaa/), value for 18 Oct 2026.
BMMAA may be quoted and reused with attribution under the terms in Data use. Live chart: Bitcoin network dashboard. First used in the BMM Mining Pools Review.