Methodology
The math behind every calculator on this site, with sources.
How calculations work, in general
Every calculator runs entirely in your browser using vanilla JavaScript. The math is in plain functions you can read in the page source. No values you type are sent to a server. There is no remote API call to evaluate.
Results are estimates. Inputs are self-reported, drinking patterns vary, and standard-drink definitions differ between countries. Where we use a specific definition (US, UK, Australia), we say so on the page that uses it.
Contents
Days sober and time alcohol-free
Given a start date S and today's date T, the number of full alcohol-free days is:
days = floor( (T − S) / 86,400,000 )
Both dates are normalized to UTC midnight before subtracting, so the number does not jump or lag when you cross a time-zone boundary. If S is in the future or invalid, the result is shown as 0 rather than a negative number.
For week, month, and year breakdowns we use a calendar approach rather than fixed-length divisors: weeks = floor(days / 7), and calendar months and years are counted by walking forward from the start date.
Money saved from not drinking
The savings calculator estimates what you would have spent on alcohol had you continued at your stated rate. The inputs are drinks per week D and average cost per drink C. The savings per period are:
- weekly = D × C
- monthly = D × C × (52 / 12)
- yearly = D × C × 52
- five-year = D × C × 52 × 5
We use 52 weeks per year rather than 365.25 / 7 to keep the math legible and the rounding stable. "Drink" means whatever the user considers a drink, a pint, a glass of wine, a cocktail, at the stated cost. We don't normalize to standard drinks here because the user is reasoning about their wallet, not their grams of ethanol.
We don't model inflation, interest, or what you might do with the money instead. Those would add false precision to a back-of-the-envelope number.
Standard drinks (US)
A US standard drink is defined by the National Institute on Alcohol Abuse and Alcoholism (NIAAA) as any drink containing about 14 grams (0.6 fl oz) of pure alcohol. To convert any beverage to standard drinks:
standard drinks = volume (fl oz) × ABV / 0.6
Equivalently in metric: standard drinks = volume (mL) × ABV × 0.789 / 14, where 0.789 g/mL is the density of ethanol.
Source: NIAAA, "What is a standard drink?"
Alcohol units (UK)
A UK alcohol unit is defined by the NHS as 10 mL (8 g) of pure alcohol. The formula:
units = volume (mL) × ABV / 1000
For example, a 175 mL glass of 12% ABV wine is 175 × 12 / 1000 = 2.1 units.
Source: NHS, "Calculating alcohol units".
Calories from alcohol
Ethanol contains about 7 kilocalories per gram (a commonly cited value; the more precise figure is 6.93). So for any beverage:
alcohol calories = volume (mL) × ABV × 0.789 × 7
This counts only the calories from ethanol. Many drinks (beer, cocktails, mixers, liqueurs) contain additional calories from carbohydrates, sugar, or cream. Where a calculator on this site shows a "total calories" figure for a specific drink type, we say which standard composition we used.
Source: USDA / general nutrition convention; see also the British Nutrition Foundation's alcohol pages for additional context.
Drinks per week
If you have a typical pattern, for example, "two drinks on weekday evenings and four on Saturday", the weekly total is just the sum. For drinkers whose intake varies day-to-day, we suggest entering an average. Most public-health guidelines (US, UK, AU) frame consumption per week, so this is the unit that maps most cleanly to guidance.
For reference, the US Dietary Guidelines define moderate drinking as up to 1 drink per day for women and up to 2 for men. The UK Chief Medical Officers' guideline is no more than 14 units per week for both. Neither is a recommendation; both are upper limits described as "lower risk."
Milestones and quit-date projections
Given a start date S, the date you'll reach N days alcohol-free is simply S + N days, with the addition done by calendar (not by milliseconds), so it lands on the same local-clock-time on the future day.
For the milestone calculator, "milestone dates" are the calendar dates of 7, 30, 60, 90, 180, 365, 730 days from S. We don't attach health-outcome claims to these, they are date arithmetic, not medical predictions.
Blood alcohol (BAC) estimate
This is an estimate. Do not use it to decide whether to drive. If you have had any alcohol, the right answer is not to drive.
The BAC estimator uses the standard Widmark formula:
BAC (g/dL) = A ÷ (W × 10 × r) − β × t
where A is grams of pure alcohol consumed, W is body weight in kilograms, r is a sex-based distribution constant (commonly 0.68 for men and 0.55 for women, with the well-documented caveat that these binary averages oversimplify real biology), β is the elimination rate (commonly 0.015 g/dL per hour), and t is hours since drinking began. The factor of 10 converts the mass fraction in body water (g per kg) to the conventional g per decilitre.
Widmark's formula was published in 1932 and is the basis for most BAC estimators in use today, but it ignores many real-world variables: food in the stomach, individual metabolism, medications, hydration, drink composition, and measurement error in your stated inputs. Two people with identical inputs can have substantively different actual BACs.
Because of that, our BAC page treats any non-zero estimate as a reason not to drive. We don't display a "you are under the legal limit" message under any circumstance.
If we got something wrong
If a formula on this page is wrong, or you have a cited correction, let us know via the contact path on sober-tracker.app. We'll update the page and note the correction.
Last updated: 18 May 2026.