The angel's share in numbers: how much whisky really evaporates, and where it goes on your returns

Everyone in whisky knows the romantic version: the angels take their share. The practical version is that evaporation is one of the biggest costs of maturation, a line on your HMRC return, and a number your insurer, your accountant and any cask buyer will ask about. Here is what the numbers actually look like.

The headline rates

A useful planning baseline for Scottish dunnage and racked warehouses:

These are planning ranges, not promises — individual casks vary enormously. But they frame the economics: fill a butt with 317.5 LPA and after 18 years you may be bottling from something closer to 240 LPA. The missing 75-odd LPA was never dutiable, never bottleable, never sellable. It is pure cost, and it is why older whisky is expensive even before scarcity and storage are counted.

What actually drives the loss

Cask size. Evaporation happens through the wood, so what matters is the ratio of wood surface to liquid. A 500-litre butt has far less surface per litre than a 190-litre barrel, so it loses a smaller percentage each year. Quarter casks and smaller mature fast partly because they breathe fast — and they pay for it in losses.

Climate. In cool, humid Scotland, ethanol evaporates slightly faster than water, so both volume and ABV drift down. In hot, dry climates (Kentucky, parts of Spain, tropical maturation) water can leave faster than alcohol, so volume plummets while ABV rises. Same angels, different appetites. This is why a Scottish regauge usually shows strength down a point or two, while a bourbon barrel can come out above its fill strength.

Warehouse type. Traditional earth-floor dunnage warehouses are cool and damp year-round: slow, steady losses and falling ABV. Modern high racked or palletised warehouses run warmer and drier, especially in the upper tiers, and tend to lose more volume. Casks in the same warehouse can behave differently by position.

Fill strength and cask condition.Higher fill strengths and older, more porous wood both nudge losses up. A poorly coopered or damaged cask is not angel's share at all — it is a leak, and it should be caught and recorded as such.

Time. Losses are usually heaviest in the first year or two (the wood soaks up spirit) and then settle to a steadier annual rate.

A worked example: one butt, eighteen years

• Fill (2008): 500 litres at 63.5% ABV → 317.5 LPA (the OLA)
• Regauge at bottling (2026): 404 litres at 58.7% ABV → 237.1 LPA (the RLA)
• Angel's share: 317.5 − 237.1 = 80.4 LPA, about 25% of the alcohol, ~1.6% a year compounded

At the February 2026 spirits duty rate of £33.99 per LPA, that 80.4 LPA would have carried about £2,733 of duty had it been released for UK sale. It never will be — which is also why duty is charged on what leaves bond, not what goes in. The angels drink duty-free.

Where the angel's share goes on your HMRC returns

The angel's share is a loss in storage on the W1 excise warehouse return. Two things matter in practice:

When it is recognised. Most distilleries recognise maturation loss when a cask is actually measured — at a regauge, or when it is emptied for vatting or bottling — as the difference between the book figure and the measured figure. Day-to-day, the book stock stays at the last known figure. That means a month in which you empty a lot of old casks will show a large storage loss, and that is normal and explainable.

Keeping it separate from operational losses.What disappeared while the cask slept is a storage loss. What disappeared in the pipework, filter and sample jar while you vatted or bottled it is an operational loss. HMRC's form asks for them on different lines, and lumping them together hides a leaky cask behind a sloppy bottling run (or vice versa).

HMRC does not publish a fixed "allowed" percentage for maturation losses, but it does expect losses to be reasonable and investigated. A clean record of regauges, with losses per cask that sit in the normal range, is what makes that conversation short.

Where angel's share accounting goes wrong

1. Never regauging, so the books carry fill figures for decades and the entire loss lands as one unexplained cliff at bottling.
2. Calling a leak the angel's share. A cask losing 5%+ a year has a fault. Recording it as routine evaporation means nobody fixes the cask.
3. Merging storage and operational losses on the W1, hiding where the alcohol actually went.
4. Forgetting samples. Every competition entry, customer sample and lab draw removes alcohol. It is a loss (or a removal), not a rounding error.
5. Assuming ABV only falls. Buy casks matured in warmer climates and your intake paperwork may show strength up — if your system refuses to accept it, the records get fudged.
6. Ignoring position effects. Top-tier racked casks losing more than ground-level dunnage is physics, not theft — but only position records let you prove it.

How Provenate tracks the angel's share

Provenate is distillery management software that treats evaporation as data, not folklore:

• Every regauge recorded per cask — OLA, current RLA, and the full measurement history, so the loss is always attributable to specific casks and periods.
• Storage losses split from operational losses automatically when a cask is vatted or bottled, exactly as the W1 asks.
• Losses flow to the W1 for you.When casks are measured or emptied, the angel's share lands on the right line of the right period, traceable to cask level — part of how your W1 builds itself.
• Outliers surfaced. Casks losing faster than their peers are flagged for inspection before they become an HMRC question or an insurance claim.

Curious what your warehouse's real annual loss rate is? Book a demo and find out from your own data.

Official sources

• Excise Warehousing: Excise Warehouse Return (W1) form and notes
• Receive goods into and remove goods from an excise warehouse (Excise Notice 197)
• Alcohol Duty rates