In short: The angel's share is the spirit lost to evaporation during aging, typically 2 to 6 percent per year and 30 to 40 percent over a long maturation, higher on upper floors and in hot, dry climates. Because the lost spirit was made from grain you paid for, modeling it per barrel turns a year-end surprise into a forecastable cost that feeds pricing and valuation.
What is the angel's share?
As whiskey ages, water and alcohol evaporate through the barrel, so volume drops over time and proof drifts depending on conditions. This loss is the angel's share. It is unavoidable, but it is also measurable and, with enough history, predictable. See the glossary definition.
How much do barrels lose per year?
Public ranges put loss at roughly 2 to 6 percent per year, totaling around 30 to 40 percent over a long maturation. The rate is not constant: hot, dry stretches pull more volume, and upper floors of a rickhouse run hotter and lose more than the ground floor. Two barrels filled the same day in different positions can end up meaningfully different.
Why the angel's share is a real cost
Every proof gallon that evaporates is spirit you cannot sell, made from grain, yeast, and barrel you already paid for and aged at your expense. Folding the loss into cost per barrel is what makes your true cost per surviving proof gallon honest, and it is often larger than founders expect over a long age.
How to forecast it
Compound the annual rate: remaining proof gallons equal starting proof gallons times (1 minus the loss rate) raised to the number of years. At 4 percent per year over 5 years, a barrel keeps about 80 percent of its proof gallons. Our angel's share calculator does this, and the barrel cost calculator turns it into cost per remaining proof gallon.
Using position data to reduce surprises
Because loss varies by floor and microclimate, tracking it per barrel against position and season builds a measured history you can forecast from, and informs where you place future fills. A 3D view of the rickhouse with per-barrel loss makes those patterns visible. See rickhouse management software.
General information, not legal or tax advice. Confirm current requirements with the TTB and your state authority. Last updated June 20, 2026.