Hello!
About DayDay
Last updated: October 14, 2026
In short: DayDay is a small team making friendly iPhone apps for everyday health. We explain the rules behind our apps in plain language, link every health fact to its source, and mark every number as the estimate it is.
What DayDay makes
- Forward, an iPhone app for losing weight with a steady calorie deficit. It adds up meals and movement into one daily number. It is in development and not in the App Store yet.
- Rest, a gentle sleep app, being built after Forward.
- Free calculators for calorie deficit, BMI, 7-day weight average and sleep times. They run in your browser and don’t send or save what you type.
How we write
- We write about our own decisions. Our blog explains why the apps work the way they do, such as why Forward shows “about 250” instead of 250, or why it leads with a 7-day weight average.
- Every health fact has a source. We link to primary research (usually on PubMed) or to public health bodies such as the NHS, the CDC, the NIH and the WHO, and list the sources at the end of each post.
- No made-up stories. We don’t publish testimonials, before-and-after claims or invented examples presented as real people. Example numbers are labeled as examples.
- No promises. We don’t promise results, because individual results vary.
- Dates are shown. Each post shows when it was published, and when we change a fact we update the post and its date.
How the numbers are worked out
The calculators on this site use the same rules as Forward:
- Calories burned at rest: the Mifflin–St Jeor equation, multiplied by an activity level. See the calorie deficit calculator.
- Deficit and pace: about 7,700 kcal per kilogram, giving paces of 0.25, 0.5 and 0.75 kg a week, never planning a day below 1,200 kcal for women or 1,500 kcal for men. See how big a calorie deficit should be.
- Goal weight: never below a BMI of 18.5 for your height. See the BMI calculator and healthy goal weight for your height.
- Weight trend: the average of every weigh-in from the last seven days. See the 7-day weight average calculator.
- Sleep times: whole cycles of about 90 minutes plus time to fall asleep, alongside the recommendation that adults get 7 or more hours. See the sleep calculator.
What we are not
DayDay is not a medical provider, and our apps and tools are not medical devices. They are for general wellness and can’t diagnose or treat anything. Talk to a doctor before big changes to what you eat, how you exercise or how you sleep. Our Terms of Use explain this in full, and our Privacy Policy explains what data we handle.
Corrections
If you spot a mistake in a post, a calculator or a source, please tell us. We’ll check it, fix it, and update the date on the page.
Contact
Questions about this page? Email us at hello@dayday.app.