Sugar Acid-Attack Calculator

What is an acid attack on your teeth?

When you eat or drink sugar or starch, the bacteria in plaque turn it into acid. That acid lowers the pH (raises the acidity) of the plaque on your teeth. Below a certain level, called the critical pH, minerals start to dissolve out of enamel. Saliva then slowly neutralizes the acid and the pH climbs back.

That dip and recovery is called the Stephan curve, after Robert Stephan's research in the 1940s. A dental education course by Higham and colleagues summarizes the classic findings: the critical pH for enamel is about 5.5, though it can vary between about 4.5 and 5.5, depending on things like the calcium and phosphate around the tooth, buffering and fluoride.

Almost any carbohydrate counts. Sugars like sucrose and glucose are the easiest for bacteria to use, but starchy foods such as crackers and bread can also be broken down.

How long does an acid attack last?

Roughly 20 minutes to an hour after each sugary food or drink. Sources give different numbers because they measure different things:

So the calculator shows two numbers for everything: a short estimate (20 minutes after you finish) and a long estimate (60 minutes after you finish). Your real time is likely somewhere in that range, and it depends on your saliva, your plaque and what you ate.

Why how often matters

Every time you eat or drink sugar, a new acid attack starts. The Oral Health Foundation puts it simply: if you snack often, your teeth have little time to recover. It advises sticking to three meals a day where you can, and keeping sugary foods and drinks to mealtimes.

Compare two days with the same treats:

• With meals: a cookie with lunch and a soda with dinner add little extra acid time, because they mostly overlap with the meals' own attacks.
• Spread out: the same cookie at 10 AM and soda at 3 PM create two extra attacks.

A review in the American Journal of Clinical Nutrition (Touger-Decker and van Loveren, 2003) notes that having sugars as part of meals rather than between meals may reduce cavity risk. The amount still matters too. The World Health Organization advises keeping free sugars below 10% of daily energy, and ideally below 5%.

Sipping and grazing: the slow attacks

A drink you sip for an hour keeps the attack going for that whole hour, plus the recovery time. The ADA explains that sipping gives bacteria more time to use the sugar, and advises finishing a drink in one sitting. Sweetened coffee at a desk, a sports drink at the gym and a juice box carried around all day are the classic examples.

The calculator's Over box handles this. Enter 60 minutes for a coffee you nurse all morning, and the acid period starts at the first sip and ends 20 to 60 minutes after the last.

Sticky and slow-dissolving foods work the same way. Hard candy, lollipops and sugary mints keep sugar in your mouth for as long as they last.

What to change first

The tool tests three kinds of change on your own day and picks the three that cut the most acid time:

1. Move it to a meal. A snack eaten with a meal mostly overlaps the meal's attack.
2. Finish it in one sitting. Turning an hour of sipping into about 10 minutes removes most of that drink's extra time.
3. Swap it. Water, unsweetened drinks or a sugar-free snack like cheese don't start an attack.

It also suggests two habits it doesn't count in the totals, because the research doesn't give a time we could model reliably:

• Sugar-free gum after eating. In a small study (Manning and Edgar, 1993), chewing gum after a sugar rinse, a snack or a meal reduced the plaque acid response, and sugar-free gum seemed most effective. The Oral Health Foundation recommends it.
• Water or milk between meals. The Oral Health Foundation recommends both as between-meal drinks.

Diet soda and flavored sparkling water aren't counted, because they have no sugar for bacteria to use. But they're acidic. The ADA notes that sugar-free carbonated drinks can still wear away enamel. This is a different kind of damage, called erosion, and this model doesn't measure it. The Toothpaste RDA Chart explains why worn enamel makes toothpaste abrasivity matter more.

Brushing straight after an acid attack isn't the answer either. The Oral Health Foundation suggests waiting at least an hour after eating. The Two-Minute Brushing Timer explains why.

How this tool works

The model, step by step:

1. Each food or drink that contains sugar or starch is an exposure. It starts at the time you enter and lasts for the Over time (0 if you finish it at once).
2. Each exposure adds an acid period: from the start of the exposure until 20 minutes (short estimate) or 60 minutes (long estimate) after it ends.
3. Periods that overlap or touch merge into one attack. A 1-minute gap keeps them separate.
4. The day is a 24-hour circle. A late-night snack's acid period carries on past midnight into the early hours, as it would on your next typical day.
5. Acid time is the total minutes covered by acid periods. Acid attacks is the number of separate periods. Both are shown as a range, short estimate to long estimate.

The acid clock has midnight at the top and runs clockwise. Dark red is the short estimate, and the lighter band shows how far the long estimate reaches. Dots mark each exposure.

Best changes: the tool tries every change (move to the nearest meal, finish in one sitting, swap out) on every non-meal item. It picks the one that removes the most minutes across both estimates, then repeats twice more, changing each item only once. Swaps count a little less when ranking, because dropping something entirely is a bigger ask than moving it. The minutes you see are always the model's real result.

Limits: real plaque pH depends on your saliva, your plaque bacteria, fluoride and the food itself. Bowen's 2013 review "The Stephan Curve revisited" points out that pH varies within plaque and warns against judging foods only by a critical pH. Treat the numbers as a way to compare days and habits, not as a measurement of your teeth. If you're worried about cavities, your dentist can assess your own risk.

Frequently asked questions

Sources

1. American Dental Association (MouthHealthy). Module 2: Plaque Attack! (Smile Smarts lesson plan). 2005. "Each acid attack can last 20 minutes.". Accessed October 26, 2026.
2. Higham S, Hope C, Valappil S, Smith P. dentalcare.com (Procter & Gamble). Caries Process and Prevention Strategies: The Environment (continuing education course CE371). last revised August 27, 2021. Summarizes Stephan and Miller's 1940s research: pH may stay below the critical level (about 5.5) for about 20 minutes and return to resting levels in about 30 to 60 minutes. Accessed October 26, 2026.
3. Oral Health Foundation. Tips to Reduce Risks of Grazing All Day. Accessed October 26, 2026.
4. Oral Health Foundation. National Smile Month: Diet and oral health. Wait at least one hour after eating before brushing. Accessed October 26, 2026.
5. Bowen WH. Odontology 2013;101(1):2–8. The Stephan Curve revisited. 2013. Accessed October 26, 2026.
6. Touger-Decker R, van Loveren C. American Journal of Clinical Nutrition 2003;78(4):881S–892S. Sugars and dental caries. 2003. Accessed October 26, 2026.
7. Manning RH, Edgar WM. British Dental Journal 1993;174(7):241–244. pH changes in plaque after eating snacks and meals, and their modification by chewing sugared- or sugar-free gum. 1993. Accessed October 26, 2026.
8. American Dental Association (MouthHealthy). Sugar, Drinks and Dental Health. Accessed October 26, 2026.
9. American Dental Association (MouthHealthy). Understanding and preventing cavities. Accessed October 26, 2026.
10. American Dental Association (MouthHealthy). 6 Ways to Reduce Your Child's Sugary Snacking. Accessed October 26, 2026.
11. World Health Organization. Sugars and dental caries (fact sheet). August 14, 2025. Accessed October 26, 2026.

Last reviewed October 26, 2026 by the Dental Health Time editorial team, against the sources above. How we review.