Faster blocks do not automatically increase mining revenue. Zcash’s proposed NU7 would shorten target block spacing while proportionally reducing the scheduled subsidy per block, keeping scheduled issuance per day approximately unchanged. Bitcoin targets a much longer average interval of 10 minutes, but block frequency alone does not determine mining profitability.
Zcash’s proposed Network Upgrade 7 (NU7) would reduce target block spacing from 75 seconds to 25 seconds. This article examines what the proposal would change, what it is designed to leave unchanged, and how the resulting mining economics compare with Bitcoin’s much longer block cadence.
As of October 12, 2026, NU7's Mainnet activation height remains unassigned in the project's draft deployment specification, ZIP 259. The protocol changes described below should therefore be read as proposed rules rather than live Mainnet behavior (ZIP 259).
Block Time Is a Target, Not a Revenue Multiplier
In proof-of-work systems, block target spacing is the average interval the protocol is designed to produce, not a guaranteed interval between any two specific blocks. Block discovery is probabilistic: miners search for a valid hash below a difficulty-defined target, and the network periodically recalibrates that target so that, over time, blocks arrive close to the intended average.
For a miner or pool with a stable share of network hashrate, expected coin-denominated revenue over a given period depends on that share and the subsidy and fees available to miners over the period. Pool fees, payout method, uptime, and rejected-share rates affect an individual miner’s realized earnings. Asset price determines the fiat value of those earnings, while electricity and other operating costs determine profitability. Network difficulty affects expected output for a given amount of hashrate; it should not be treated as an additional independent revenue multiplier once hashrate share and network rewards over the period are fixed. Changing the number of block opportunities without changing the total reward pool redistributes when rewards arrive; it does not, by itself, create additional value.
What NU7 Proposes to Change
ZIP 218 specifies three linked changes to Zcash's issuance schedule, designed to move together:
- Block target spacing falls from 75 seconds to 25 seconds, roughly tripling the target number of blocks per day—from 1,152 to 3,456, based on dividing 86,400 seconds in a day by each target spacing.
- Scheduled block subsidy is divided by three. ZIP 218 gives a direct illustration for the current halving period: the pre-NU7 scheduled subsidy of 1.5625 ZEC per block becomes 0.52083333 ZEC per block after NU7, subject to zatoshi rounding.
- Full halving interval, measured in blocks, is tripled—from 1,680,000 post-Blossom blocks to 5,040,000 blocks. The transition also accounts for progress already made through the current halving period, scaling the remaining block count so that halvings continue to occur on roughly the same wall-clock schedule rather than three times sooner (ZIP 218).
ZIP 218 also increases Zcash’s difficulty-averaging window from 17 blocks to 102 blocks at NU7 activation. At the current 75-second target, 17 blocks span 1,275 seconds; at the proposed 25-second target, 102 blocks span 2,550 seconds. This doubles the current nominal time window and restores the duration originally used when Zcash targeted 150-second blocks (ZIP 218).
Why Scheduled Issuance Per Day Is Designed to Stay Constant
Letting S represent the pre-NU7 scheduled subsidy per block, the arithmetic is straightforward: 1,152 blocks per day at subsidy S yields 1,152S in scheduled daily issuance before NU7; 3,456 blocks per day at subsidy S/3 yields 3,456 × (S/3) = 1,152S after NU7. The two totals are equal by design.
This is a simplified, article-specific calculation based on target spacing alone. It excludes transaction fees, Zcash's funding-stream allocations, rounding at the block level, price movements, difficulty changes, pool fees, and operating costs—all of which affect what a miner actually realizes. The correct framing is that NU7 is designed to preserve the scheduled subsidy issued per unit of calendar time, not that it guarantees any particular miner's realized revenue will be unchanged.
Zcash has precedent for this kind of transition. The earlier Blossom upgrade reduced target spacing from 150 seconds to 75 seconds; ZIP 218 notes that, under the prior 17-block averaging window, the rolling average block interval reached approximately 74 seconds only 64 blocks after activation. The target changes at activation, while observed block intervals converge toward it as difficulty adjusts.
Bitcoin's Cadence and Difficulty Adjustment
Bitcoin targets an average block interval of 10 minutes and recalculates difficulty every 2,016 blocks, using the elapsed time of the preceding interval against an intended span of 1,209,600 seconds, or two weeks (Bitcoin Developer Documentation). This differs structurally from Zcash's approach, which recalculates difficulty after every block using a DigiShield-derived averaging method.
The practical implication is that Bitcoin and Zcash should not be compared as though a shorter block interval universally produces a different economic outcome. The two networks operate on different cadences for both block production and difficulty adjustment, and Bitcoin's block reward—subsidy plus transaction fees paid in full to the block's miner—differs from the fee-allocation model NU7 proposes for Zcash, discussed below.
Where Mining Economics Actually Change
Reward timing and variance
Even when scheduled issuance per day is held constant, the distribution of that issuance across block events changes. Under a simplified Poisson model with a fixed hashrate share, a fixed observation period, and an unchanged miner allocation percentage, tripling the expected number of blocks found while dividing the subsidy received per block by three leaves expected subsidy earnings unchanged. The variance of those earnings falls to one-third of its previous value, and the standard deviation falls to 1/√3 of its previous value—a reduction of approximately 42.3%.
This result describes subsidy earnings over a fixed period for solo mining under specific simplifying assumptions; it ignores stale or orphaned blocks, fee variability, and price movement. It does not translate directly into a 42.3% reduction in payout volatility for pool participants. Pool payout variance also depends on pool size, pool luck, payout method (such as PPS+ or PPLNS), share-difficulty settings, and the pool's accounting rules, and should not be inferred from the solo-mining calculation alone.
Fee allocation under NU7
NU7's proposed fee rule, specified in ZIP 235, is a separate and economically material change. Under the proposal, 60% of the aggregate transaction fees in a block would be allocated to the Network Sustainability Mechanism (NSM) and removed from direct miner compensation; the remaining 40% would be retained as miner fees, with rounding in the miner's favor at the block level (ZIP 235).
This differs from Bitcoin, where the block reward is generally described as the block subsidy plus the full transaction fees included in that block. A post-NU7 Zcash miner would not receive the same share of transaction fees as a Bitcoin miner receives today; the NU7 fee-allocation rule, not only the shorter block interval, materially affects what miners actually collect from each block.
ZIP 237, also included in the NU7 deployment draft, specifies how ZEC removed from circulation would later be reissued as additional block subsidy while preserving the four-year halving structure. The NSM Value Balance is a consensus-tracked accounting balance, not a spendable reserve. Reissuance begins at a separate height calculated under ZIP 237, after the third halving and before the fourth under the draft’s deployment conditions. Its exact Mainnet height depends on the final NU7 activation height. Future reissuance should not be treated as an immediate, block-for-block offset to redirected fees (ZIP 237; ZIP 259).
Block propagation and stale blocks
As block target spacing falls, the time available to propagate a newly found block before a competing block is found also falls, making propagation performance more economically relevant. ZIP 218 reports a theoretical stale-block rate of approximately 3.26% at a 25-second target, derived from measured Zcash propagation delays, and a separate development-network test—99 Zebra nodes across 14 regions producing 2 MB blocks at a 25-second target—that measured a 4.86% stale-block rate and a 0.37% fork rate (ZIP 218).
These figures are development-network and model-derived results, not Mainnet measurements, and they should not be treated as a forecast of any individual miner's experience. It is also important to keep terminology distinct: a stale block is a chain-level outcome determined by network propagation, while a stale or rejected share is a pool-side submission outcome reported to an individual miner. The two are related in concept but are not the same measurement and should not be merged.
What Miners and Pool Users Should Monitor
Regardless of block target spacing, the inputs that determine realized mining revenue remain the same categories of data, though the specific figures reported will differ by network:
- pool-estimated hashrate, reported over a stated rolling window, as distinct from local or device-reported hashrate;
- rejected-share rate and the stated reasons for rejection;
- payout records and the pool's fee structure and payout method;
- network difficulty, asset price, and actual (not scheduled) transaction fees collected;
- uptime and power consumption measured on the mining hardware itself.
When evaluating a pool's reporting, it is worth confirming how these figures are defined and over what time window they are calculated, since pool-side estimates, miner-side telemetry, and realized payout records are related but distinct categories of data.
Conclusion
NU7's proposed reduction in Zcash's block target spacing, from 75 seconds to 25 seconds, is paired with a proportional reduction in the scheduled subsidy per block and an adjustment to the halving schedule that triples the full interval and scales the remaining block count at activation. Taken together, these changes are designed to preserve scheduled ZEC issuance per unit of calendar time rather than to increase it. The economically meaningful effects of NU7 lie elsewhere: in how reward variance is distributed across more frequent, smaller events; in the 60/40 fee-allocation split introduced by ZIP 235, which changes how much of a block's transaction fees miners actually retain; and in the greater importance of block propagation as the window between blocks narrows. Bitcoin's much longer target spacing and periodic difficulty-adjustment design make it a useful point of contrast rather than a direct basis for comparing hashrate or revenue figures across the two networks. Faster blocks change timing and operational considerations more than they change scheduled issuance per day.
FAQ
Does NU7 increase the total amount of ZEC miners can earn per day?
Not simply because blocks arrive faster. The proposed spacing change divides the scheduled subsidy per block by roughly three while tripling the target number of blocks per day, keeping scheduled ZEC issuance per day approximately unchanged. A miner’s actual ZEC earnings also depend on hashrate share, funding allocations, transaction-fee rules, pool terms, and operating performance. ZIP 237 separately provides for additional NSM subsidy at a later reissuance height; asset price affects the fiat value of earnings, not the number of ZEC received by itself.
Will Zcash miners receive all transaction fees after NU7?
Under the proposal, no. ZIP 235 specifies that 60% of a block's aggregate transaction fees would be allocated to the Network Sustainability Mechanism, with the remaining 40% retained as miner fees.
Is a shorter block target spacing the same as lower mining risk?
Not directly. A simplified model suggests tripling block opportunities while proportionally reducing the per-block subsidy can lower the variance of solo subsidy earnings over a fixed period, but pool payout variance depends on additional factors, including pool luck, payout method, and fee structure, and should not be assumed to fall by the same proportion.
Can Bitcoin and Zcash mining revenue be compared directly because one has faster blocks?
No. The two networks use different difficulty-adjustment designs, different fee-allocation rules, and different target spacings, so comparing raw block frequency or hashrate between them does not produce a meaningful revenue comparison.
Has NU7 activated on Zcash Mainnet?
As of October 12, 2026, ZIP 259 still lists NU7’s Mainnet activation height as TBD. The rules discussed here remain proposals rather than live Mainnet behavior. A finalized activation height would specify when activation is scheduled; it would not by itself mean the upgrade had already activated.
References
Sources checked October 12, 2026. NU7 specifications remain drafts and should be rechecked before publication.