Trendline is an iPhone app that reads Apple Health. If you're here because you want Happy Scale on Android: neither app runs there — the established Android choice for moving-average weight tracking is Libra. Everything below is iPhone territory.
First, the honest part
Happy Scale has earned its reputation: a 4.9-star average across roughly 58,000 App Store ratings, active development for over a decade, local-first storage with no vendor account, and free import of weight entries from Apple Health (its App Store listing, checked July 2026). Its core idea — show a smoothed moving average so one salty dinner can't ruin your morning — is the same measurement literacy Trendline is built on. If you want exactly that, well-executed, you can stop reading and be in good hands.
The one design choice to understand
Happy Scale's own documentation states that it imports one weight per day — the lowest entry, as its chosen way to estimate the moving average (Happy Scale support FAQ). That is a legitimate, documented modeling decision, and for many people it's fine.
Trendline makes the opposite choice: every reading is kept, with its timestamp, source, and unit. Nothing about your day is discarded or selected. Two consequences follow. Practically, morning and evening readings, multiple sources, and dense histories all survive intact. Epistemically, the trend is computed from what actually happened rather than from a per-day selection rule — and when your data is sparse, Trendline says the evidence is thin instead of drawing an equally confident line. The full math is public on the methodology page.
Where the two apps genuinely differ
| Happy Scale | Trendline | |
|---|---|---|
| Daily readings | One per day imported (lowest), per its FAQ | Every reading kept, with provenance |
| Trend method | Smoothed moving averages | Statistical trend with explicit uncertainty; declines to conclude when evidence is sparse |
| Sparse data | Averages continue from available entries | Says "not enough to say" rather than projecting confidence |
| Energy (TDEE) | Not offered | Not in the current iPhone app; a separate free browser calculator is available on this site |
| Composition metrics | Weight-focused | At launch: manual entry for composition values beyond Apple Health's types (visceral fat, body water, muscle mass…) |
| Accounts | None required; local-first, optional Dropbox/iCloud sync | None required; Apple Health is the only "account" |
| Pricing | Free tier; Deluxe $1.99/mo, $11.99/yr; lifetime $39.99 (App Store listing, July 2026) | $1.99/week · $5.99/month · $39.99/year · $99.99 lifetime |
Read that pricing row plainly: Happy Scale is substantially cheaper over time, and its one-time lifetime unlock costs about the same as a single year of Trendline at the prices checked above. If price alone decides it, Happy Scale wins outright and we won't pretend otherwise. What the difference buys is a different product: every reading kept rather than one per day, Lose/Build/Maintain as distinct phases, body-composition context, and a trend that states its uncertainty instead of hiding it. Whether that difference is worth paying more is exactly the decision this page exists to help you make honestly — and for a lot of people the answer will be no.
Who should pick which
- Pick Happy Scale if you want a mature, single-purpose moving-average tracker today, love its milestone/prediction features, and one reading per day matches how you weigh.
- Pick Trendline if you keep multiple readings or sources, want the trend to admit uncertainty, want losing, building, and maintaining treated as different jobs, or want your scale's composition estimates kept in context.
Try the idea
The core disagreement — what a trend should do with your raw readings — is testable right now: paste your weights into the free weight trend calculator and see the slower signal drawn against every single reading, nothing discarded.
Sources
- Happy Scale on the App Store (v2026.5.3, pricing and Health-import statements)
- Happy Scale support FAQ (one-weight-per-day import, storage model)
Trendline is not affiliated with or endorsed by Happy Scale or Front Pocket Software. Facts above were verified against the linked pages on July 20, 2026; app stores change — check the listing for current pricing.