A – Z
These are the terms you'll encounter across DayByDay — in the app, in your data, and in this help center. Definitions are kept short and jargon-free on purpose.
A1c (HbA1c)A blood test that shows your average blood sugar level over the past 2–3 months. Reported as a percentage. Lower is generally better for people managing blood sugar.Active caloriesCalories burned through movement and exercise, on top of what your body burns at rest. Synced from Apple Health.AHI (Apnea-Hypopnea Index)The number of times per hour you stop breathing or have significantly reduced breathing during sleep. AHI is the main metric for diagnosing sleep apnea. DayByDay does not currently track AHI directly — it focuses on blood oxygen and sleep stages instead.Apple HealthApple's built-in health data platform on iPhone and Apple Watch. DayByDay can read weight, steps, sleep, workouts, and heart rate from Apple Health automatically (set it up in You → Health Sync).BMI (Body Mass Index)A number calculated from your weight and height. It is a rough screening tool — not a precise measure of health. Muscle, age, and ethnicity can all affect whether BMI accurately reflects your body composition.BMR (Basal Metabolic Rate)The number of calories your body burns just to stay alive at complete rest. Think of it as your body's idle speed. DayByDay calculates this using the Mifflin–St Jeor equation.Body fat percentageThe proportion of your total body weight that is fat tissue. You can log this manually (from a smart scale or DEXA scan) or let DayByDay estimate it using your waist and height measurements.Bookmark (flag for your appointment) 🔖The bookmark icon on any Insights card. Tap it to flag that insight for your next appointment — flagged items are collected under "For your provider" and included automatically in your Health Report PDF. It's the heart of the doctor-conversation loop.Core (plan)DayByDay's middle tier — the analysis layer. It unlocks trend charts and projections, Dayo the AI coach, Journey Mode, Apple Health sync, PDF and CSV exports, and health scores. Every new account gets a 14-day free trial of Plus, which includes everything in Core.Core sleepLight sleep stages (N1 and N2) that make up the bulk of a typical night. Core sleep is important for memory consolidation and general rest, though deep sleep and REM are considered higher quality.DayoYour AI coach — a friendly sun mascot powered by Anthropic's Claude. Each morning Dayo reads your real data and writes a short, plain-language note (your daily read), plus a fuller weekly Story in the Insights tab. Every claim is grounded in a real fact from your own data. A companion, not a doctor.Deep sleepThe most physically restorative stage of sleep (N3, also called slow-wave sleep). Your body repairs tissue, builds bone, and strengthens the immune system during deep sleep.DEXA (DXA scan)A clinical body-composition scan that precisely measures fat, lean mass, and bone density. If you've had one, you can store the results under Weight → Body → DEXA to track changes over time and share them in your report.Drops per hour (oxygen dips)The number of times per hour your blood oxygen level drops by 3% or more during sleep. A high drops-per-hour count can be a sign of sleep-disordered breathing.Trend line (rolling average)A rolling average of your last 7 weigh-ins — the smoothed line on your weight chart (labeled "trend") that filters out daily noise so you can see the direction your weight is really moving, without chasing the day-to-day bounce.EWL (Excess Weight Loss)A way to measure weight loss relative to how much you had to lose, expressed as a percentage. Losing half of your excess weight = 50% EWL. Common in GLP-1 research.FatSecretThe food database that powers the Nutrition tab's food search, barcode scan, and nutrition-label reads. It supplies the macros (protein, carbs, fat, fiber, calories) for the foods you log.FFMI (Fat-Free Mass Index)Like BMI but for muscle and lean tissue. It tells you how much of your weight is functional mass rather than fat. Useful for tracking whether you are preserving muscle during weight loss.Free (plan)DayByDay's no-cost tier. You can log everything — weight, GLP-1 doses, sleep, exercise, labs, measurements, mood — with no time limit. The analysis layer (charts, Dayo, exports) lives in Core and Plus.GLP-1GLP-1 stands for glucagon-like peptide-1. GLP-1 medications (like Ozempic and Mounjaro) mimic a natural gut hormone that slows digestion and reduces appetite. They are injected weekly or daily depending on the medication.Goal weightThe target weight you set during onboarding. DayByDay uses this to calculate your progress percentage and to estimate when you might reach it based on your current trend.Journey ModeDayByDay's signature warm sunrise-to-sunset interface — designed to make checking in feel like a reward. It's one of three looks (alongside standard Light and Dark) and is part of Core. Switch it on in You → Appearance.Lean mass / Fat-free massThe part of your body weight that is not fat — including muscle, bone, water, and organs. Preserving lean mass while losing fat is the goal of most weight loss programs, and a particular focus on GLP-1 therapy.Metabolic ageAn estimate of how old your metabolism is compared to population averages. A metabolic age lower than your actual age generally indicates a faster metabolism and healthier body composition.Momentum ScoreThe 0–100 ring on your Today tab. It blends up to seven signals — sleep, hydration, activity, medication adherence, weight trend, calories, and protein — into one friendly gauge of which way you're heading, counting only the signals you actually track. It's a nudge, not a grade; a low number just means there's an easy win waiting.NutritionDayByDay's food-logging tab (part of Plus), built around protein and fiber. Add food by searching FatSecret, snapping a photo of your plate, scanning a barcode, or scanning a nutrition label. Manual entry is free.O2 RingA finger-worn device made by Wellue/Viatom that tracks blood oxygen (SpO2) and heart rate continuously overnight. DayByDay can import data from the Wellue app to give you detailed overnight oxygen analysis.O2 ScoreDayByDay's summary score for your overnight blood oxygen quality. It factors in your average SpO2, how many oxygen dips you had, and your lowest recorded level. Higher is better.Plus (plan)DayByDay's top tier. It includes everything in Core plus the full Nutrition module (FatSecret search, barcode, photo-of-plate, label scan) and the nutrition-aware version of Dayo that connects protein to muscle, fiber to GI side effects, and energy balance to weight.Prior Authorization (PA)Approval your insurance requires before it will cover certain medications — most GLP-1s need one, often renewed yearly. DayByDay's Pharmacy & Refills screen lets you record your PA expiry date and get a reminder weeks before it lapses, so coverage doesn't lapse mid-journey.REM sleepRapid Eye Movement sleep — the stage where most dreaming happens. REM is critical for emotional regulation, memory, and learning. You cycle through REM several times a night, with longer periods toward morning.Resilience ScoreA normalized 0–100 score based on your heart-rate variability — a read on how well your body is recovering and handling stress. It appears once you've synced enough HRV data, and is part of the Core health scores.Resting heart rateYour heart rate when you are fully at rest — typically measured in the morning before getting out of bed. A lower resting heart rate is generally associated with better cardiovascular fitness.RFM (Relative Fat Mass)A body fat estimate calculated from your height and waist circumference. More accurate than BMI for most people because it accounts for where fat is actually distributed on your body.Rotation AdvisorThe GLP-1 injection-site helper. It tracks where you've recently injected and suggests your next site (e.g. "Left Upper Arm") so you rotate across zones and avoid hitting the same spot — which is easier on your skin and tissue.SemaglutideThe active ingredient in Ozempic (for diabetes) and Wegovy (for weight loss). It is a weekly injection that mimics the GLP-1 hormone to reduce appetite and slow digestion.Sleep ScoreA normalized 0–100 score summarizing the quality of your night — duration, stages, consistency, and interruptions rolled into one number. It appears after a handful of nights of stage data and is part of the Core health scores.SpO2Blood oxygen saturation — the percentage of your red blood cells that are carrying oxygen. A healthy level at rest is typically 95% or above. During sleep, brief dips are normal, but frequent drops can signal breathing issues.StreakThe number of consecutive days you've logged at least one data point. DayByDay tracks a few — Check-in, Active, and medication adherence — on your Today tab as gentle motivation. Consistency, not intensity, is what gets you there.TDEE (Total Daily Energy Expenditure)The total number of calories your body burns in a day, including both your resting metabolism and all physical activity. DayByDay estimates this by applying an activity multiplier to your BMR.TirzepatideThe active ingredient in Mounjaro (for diabetes) and Zepbound (for weight loss). It is a weekly injection that targets both GLP-1 and GIP receptors, making it a dual-action medication.TitrationThe process of gradually increasing your medication dose over time, usually in steps of several weeks. GLP-1 medications are titrated slowly to minimize side effects like nausea.Trend lineA smoothed line on your weight chart that shows the direction your weight is moving, filtering out daily noise. DayByDay calculates this as a rolling average of your last 7 weigh-ins — about a week for daily loggers.WHtR (Waist-to-Height Ratio)Your waist circumference divided by your height. A ratio under 0.5 is generally considered healthy for most adults. It is a simple way to gauge whether abdominal fat is at a concerning level.
