iPhone Screenshots


Easier and more accurate than calorie counting.

Cmac47 says: "I am a health coach and fitness professional of 25+ years ... the easiest weight loss app that I have seen ... I use [Pertinacity] with my clients"

In-Shape Health Clubs calls Pertinacity "astonishingly easy to use".

Dean G. says: "I began using the Pertinacity app [recently] and so far have lost about 5-7 pounds ... an approach that I could implement long-term."

* Track all food the same, simple way -- restaurant, packaged, or home-made.
* Solid foundation in weight-management research.
* Immediately ready and easy to use: No need to record activity, tweak calorie targets, create an account, or even configure the app.

We love email: feedback@pertinacity.org



Pertinacity shrewdly trades precision for simplicity. Studies show that increased simplicity improves adherence which improves results. [1] Your typical interaction with Pertinacity will last only a few seconds:

1) Imagine squashing a food item.
2) Make a fist. Estimate how many fists would be the same size as the
squashed food item.
3) Tap the '+' button to record the number of fists estimated.

This is calorie counting by proxy.

While less precise than calorie counting, it is still about as precise as Jawbone UP's estimation of calories expended. [2,3] And it's slightly more precise than Fitbit Ultra's or Nike Fuelband's estimates of calories expended. [2,3]

When your fist-sized portions decrease, your calories decrease. [4] When your calories decrease, your weight decreases. [5]

Pertinacity works better because it's easier to stick to.

Install now and try it by recording your next meal.


With Pertinacity you won't need to guess how many pounds/week you should lose or to tweak your daily calorie target until you see results.

Pertinacity is more accurate than typical calorie counting apps and websites because of the way it calculates your daily portion target. Your daily portion target is an average of the past two weeks of your portion counts.

This apples-to-apples comparison of *your* current count to *your* previous counts defeats the well-known biases that reduce the accuracy and effectiveness of other calorie counters:

* Calorie target formulae based on age, weight, etc. have an individual bias with an average of 200 calories. [6]
* People tend to under-report calories consumed by about 18% or around 400 calories. [7]

Pertinacity's two-week average accurately accounts for your metabolism, activity level, and tendency to underreport consumption since it's computed directly from the data you collect. And since it uses only the prior two weeks' data it automatically adapts to changes over time in your body and behavior.

Pertinacity provides clear guidance because it's automatically tuned to you.

Install now to see how quickly you can start counting.

[1] Cunningham, B. Smart Phones and Dietary Tracking: A Feasibility Study. ASU Electronic Dissertations and Theses, 2011.
[2] Stackpool, Caitlin M. Accuracy of various activity trackers in estimating steps taken and energy expenditure. UW-L Master's Theses, 2013.
[3] Correlations, Pertinacity Blog, http://www.pertinacity.org/blog/2014/3/10/correlations
[4] Dynamics, Pertinacity Blog, www.pertinacity.org/blog/2014/2/12/dynamics
[5] Sacks FM, Bray GA, Carey VJ, et al. Comparison of weight-loss diets with different compositions of fat, protein, and carbohydrates. N Engl J Med. 2009;360(9):859-73.
[6] Institute of Medicine of the National Academies. Dietary reference intakes for energy, carbohydrate, fiber, fat, fatty acids, cholesterol, protein, and amino acids. 2002, 2005
[7] Mertz W, Tsui JC, Judd JT, et al. What are people really eating? The relation between energy intake derived from estimated diet records and intake determined to maintain body weight. Am J Clin Nutr. 1991;54(2):291-5.

What's New

Version 1.2.0

Expanded and revised instructions
UI improvements

Ratings and Reviews

5.0 out of 5
8 Ratings
8 Ratings

This App Works!!

This app really works for losing weight!! I’ve tried everything over the years like working out, counting calories etc. and even when I’d lose weight I’d gain it all back. With this method of portion control, I can eat whatever I want and still keep my weight down. It hasn’t even been a month yet since I started using it, and I’ve lost 5 lbs already. Cheers for Pertinacity! What a simple, easy to use, and great app!! 😊



Simple, no frills app. It sets a baseline of portions after you record for 4 days. Then gives you a gain and a lose number. That number changes as your overall portions change. Easy to use.


Very easy!

Great and easy to use. Much better than counting calories. I use it much longer than anything else with more success because you can eat what you want. Just smaller portions.


David Sweet
1.1 MB
Health & Fitness
Requires iOS 6.0 or later. Compatible with iPhone, iPad, and iPod touch.
English, Arabic, Catalan, Czech, Danish, Dutch, Finnish, French, German, Greek, Hebrew, Hungarian, Indonesian, Italian, Japanese, Korean, Malay, Norwegian Bokmål, Polish, Portuguese, Romanian, Russian, Simplified Chinese, Slovak, Spanish, Swedish, Thai, Traditional Chinese, Turkish, Ukrainian, Vietnamese
Age Rating
Rated 4+
© 2013, 2014 David Sweet


  • Family Sharing

    With Family Sharing set up, up to six family members can use this app.

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