The habit · Decision 9 of 12

Rewards, and what we will not give one for

The app gives rewards for reaching milestones. Every one of them is visible in the menu, earned or not. The list of what is deliberately left out is the part of the design that needed the research.

Written and maintained by Mattias Geniar. Last updated .

What the app does
Rewards logging, not eating less. The biggest ones count weeks in which you logged five days, and one of them is for logging a day that went over.
How sure we are Fair , Real, but small, indirect, or thinly measured.
One review found 0.70 kg more weight loss on average with gamification; this is not a prediction for Snapkin. That is small enough that no reward is worth the risks on the eating disorders page.

The evidence for it

The first number is a pooled average, not an upper limit or a promise. The other findings inform our design choices.

−0.70 kg average weight difference with gamified versus non-gamified health-app interventions Nishi et al. (2024) · 17 body-weight trial comparisons · 95% CI −1.18 to −0.22
> 3 days a week of consistent logging was associated with less weight regain; this was not a randomized test of a minimum dose Peterson et al. (2014) · 220 women, 18 months · moderation P = 0.004
5,526 posts from three food-journaling forums, analysed for barriers and negative experiences Cordeiro et al. (CHI 2015) · plus 141 people surveyed

How much a reward is worth, which is not much

Nishi et al. (2024) compares gamified health-app interventions with non-gamified controls. Designs and accompanying support varied; this is not a trial of our badges. It covers 36 trials, 49 comparisons and 10,079 people, each lasting eight weeks or more.

Average weight difference associated with adding game elements Body-weight analysis: 17 trial comparisons. The entire review covered 36 trials and 10,079 participants across different outcomes.
no difference
Adding game elements, body weight −0.70 kg

Nishi et al. 2024, 95% CI −1.18 to −0.22, over eight weeks or more

−1.4 kg +0.4 kg
The authors rated the body-weight evidence moderate certainty. The pooled difference was −0.70 kg, with a 95% confidence interval from −1.18 to −0.22 kg. Other analyses found −0.28 kg/m² in BMI, −1.92 percentage points in body fat and 489 additional steps/day. These are averages across different interventions and outcome samples, not maxima or forecasts for an individual.

Why the rewards are for logging rather than for eating less

Peterson et al. (2014) followed 220 women through six months of treatment and twelve months of follow-up care. How often people logged predicted their weight change only when they logged consistently every week (moderation P = 0.004). The threshold they report is more than three days a week. In the same analysis, the analysis did not detect an association between entry completeness and weight change (P > 0.05).

This observational analysis supports making regular logging easier, but does not prove that incomplete logs are equally effective. Our five-day threshold is a product choice. Accordingly, the largest group of rewards here counts weeks in which you logged five days, and the biggest ones count total days logged, added up over time. The study does not establish that a daily streak is necessary.

Why almost nothing here is a streak

Cordeiro et al. (CHI 2015) surveyed 141 current and former food journalers and analysed 5,526 posts across three apps' community forums. Participants described missed entries snowballing into abandonment. We took this as a reason to support returning after a gap, not evidence that a particular streak design causes harm.

The same paper found that the feedback already feels unfair before anybody adds a game to it. One participant described guilt after exceeding a goal without equivalent satisfaction below it.

There are four streak rewards in the app, all of them for logging and none for eating. They measure your best run ever rather than the current one. Breaking a streak costs you the next one. It cannot take away one you already have.

What we refuse to give a reward for, and why

The rule, stated as a rule Nothing in the right-hand column is a feature we have not got round to.

Gets a reward

  • Logging a day at all
  • Weeks in which you logged five days
  • Total days logged, added up over time
  • Your best run of consecutive days, ever
  • Logging a day that went over your target
  • Reaching protein and staying within the calorie target band
  • Reaching protein and staying within the calorie target band

Never gets a reward

  • A calorie deficit
  • A weight, or an amount lost
  • Staying under the added sugar limit
  • A “perfect” day, week or anything else
  • Eating progressively further below your target
The calorie reward is a range with a minimum as well as a maximum: a day at 60% of your target fails it exactly as a day at 140% does. We state this as our own rule rather than as a comparison. Other trackers do reward deficits and weight lost, but the lists of their badges we could find are only in third-party copies of help pages that have since been taken down, and this page does not make claims about anybody else's product on that basis.

Nothing here is called “perfect.” Messer et al. (2021) surveyed 1,357 people. Those using a calorie app to control their weight and shape were more likely to say the app had harmed them than those using one for health reasons. The harms they named: being preoccupied with food, all-or-nothing thinking about food, anxiety about food, and purging. Plateau et al. (2018), 352 people, found the same split using different questionnaires. Motive was associated with reported harm in these surveys; it cannot identify who will be harmed or establish causation. Avoiding a “perfect day” badge is our precaution, not a proven preventive intervention.

And there is still no reward, streak or celebration on the added sugar limit, which is the promise the eating disorders page already makes. We have not tested whether attaching a streak to a dietary limit increases harm; we avoid it as a precaution. Adding a rewards screen did not change our mind about it.

The one reward that looks odd is deliberate: you get one for logging a day that went over your target. A log with the heavy days missing is not a log. An app that is only pleasant to open when the day went well stops being told the truth.