Night-Out Planner

How Much Can You Drink Tonight?

How the Night-Out Planner Works

Most BAC calculators work forward: you tell them what you drank, and they tell you your BAC. The Night-Out Planner works in reverse using the same Widmark formula — you tell it when you need to drive and what the legal limit is, and it calculates how much you can drink to stay legal.

The formula behind it: maxAlcohol(g) = (targetBAC + hours × 0.015) × weightKg × r × 10 — where r is 0.68 for men and 0.55 for women (body water distribution factor). The food multiplier then adjusts absorption, and the result is divided into standard drink equivalents (14g of pure alcohol each in the US standard).

One critical point: this tool gives you a mathematical maximum, not a recommendation. The legal limit is not a safe limit — impairment begins at BAC levels well below 0.08%. Two people with the same calculated limit can have very different real-world impairment based on tolerance, fatigue, medication, and other factors.

Why Planning Ahead Beats Guessing

The most common mistake people make when drinking and driving is trusting how they feel. Alcohol impairs your ability to assess your own impairment — the prefrontal cortex (judgment) and amygdala (self-awareness) are among the first brain regions affected. At 0.04–0.05% BAC, most people feel perfectly fine while reaction time and divided attention are already measurably degraded.

Knowing your limit before the night starts gives you a concrete number to work with instead of a subjective feeling. It lets you pace yourself, plan your last drink, and arrive at drive-time with a BAC you can be confident about rather than guessing.

How Food Changes Your Limit

Eating a substantial meal — particularly one rich in protein and fat — before drinking can meaningfully increase your effective drink limit by slowing alcohol absorption into the bloodstream. A heavy pre-drinking meal (e.g., a steak dinner) can reduce peak BAC by roughly 35% compared to drinking on an empty stomach. This works by slowing gastric emptying, meaning alcohol reaches the small intestine (where most absorption occurs) more gradually.

Critically, food affects absorption but not elimination. Your liver still clears alcohol at the same ~0.015% per hour regardless of what you ate. Food buys you a lower peak and a more gradual curve — it does not speed up how fast you sober up once alcohol is already in your bloodstream.

The 0.08% vs. 0.05% Difference

If you're in the US or UK, the legal standard is 0.08%. In most of Europe and Australia, it's 0.05%. That difference translates to roughly one full standard drink less for an average-sized adult. A 175 lb man who can have 4 beers under a 0.08% regime can only have 3 under a 0.05% regime — planning ahead is even more important in stricter jurisdictions.

Several US states are considering moving to 0.05% (Utah already did in 2018). If you drive internationally, always check the local limit before assuming your home country's standard applies.

What Counts as One Standard Drink?

In the US, one standard drink contains 14 grams of pure alcohol. This is equivalent to: 12 oz regular beer (5% ABV) / 5 oz glass of wine (12% ABV) / 1.5 oz shot of spirits (40% ABV). These are smaller than what you'd typically be served at a bar — a pint of beer (16 oz) counts as 1.3 standard drinks, and a generous pour of wine (6–7 oz) counts as 1.2–1.4 standard drinks. The Night-Out Planner uses US standard drink definitions for all calculations.

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