How we set our reminder defaults

lindly’s reminders are meant to be a calm safety net: an occasional “it’s been a while — all good?” that you can dismiss in a tap, not a stream of alarms. For that to work, the numbers behind them have to be right. Fire too early and the app becomes background noise you learn to ignore. Fire too late and the safety net has a hole in it.

So before we shipped a single default, we did a cited research pass on the three time-gap rules — no wet diaper, no feed, and no sleep — and made every threshold scale with the baby’s age. Here’s how we got there.

Not medical advice. lindly is not a medical device and doesn’t diagnose anything. A fired reminder is a prompt to glance, not a verdict. If you’re ever worried about your baby, contact your pediatrician or midwife — that’s always the right call, regardless of what any app says.

Three principles

Fire late, not early. “No gamification, no anxiety” is a design rule for us, and false alarms are the failure mode we most wanted to avoid. Whenever the evidence gave a range, we picked the conservative, later end.

Counts, translated to gaps. Almost all authoritative guidance is framed as counts per 24 hours — for example, the American Academy of Pediatrics notes a well-hydrated baby produces six or more wet diapers a day by the end of the first week. Our engine, though, watches a single gap (“no wet diaper in X hours”). Translating a daily count into a maximum tolerable gap is itself a judgment call, because the longest normal gap is always longer than the average one. We did that translation deliberately and conservatively rather than pretending a count is a gap.

Age changes everything. A newborn and a one-year-old are different bodies on different schedules, so a single flat number can’t be right for both.

Why “no feed” follows the newborn rule closely

Feeding is the one place where an earlier nudge is sometimes the medically correct action. For a newborn in the first couple of weeks, the guidance is clear and consistent across sources — don’t let the baby go longer than about four hours without feeding until birth weight is regained — so our newborn default honors that directly. As babies grow and feeds naturally space out, the threshold widens: the CDC and AAP both describe intervals lengthening through the first year, and by then a long stretch — including sleeping through the night — is healthy, not a concern. One reassuring consequence: cluster feeding can never trip this rule, because more frequent feeding only resets the timer.

Why the wet-diaper rule pierces the quiet

We hold most overnight nudges until morning. The exception is no wet diaper, the one signal we treat as worth waking for, because fewer wet nappies is a recognized early sign of dehydration in the guidance from bodies like the NHS and the World Health Organization. Even so, we set the thresholds with headroom so a normal night — where an older baby sleeps long and simply isn’t changed — doesn’t fire a false alarm at dawn. The younger the baby, the shorter we allow the gap, because young babies are changed overnight anyway and a genuinely long dry stretch is more unusual.

Why we rejected a flat 24 hours

A single “no wet diaper in 24 hours” rule is a tempting default, and it’s wrong in both directions.

For a newborn, 24 hours is dangerously late — a day-old baby with zero output for a full day is a serious situation, and a rule that only speaks up at 24 hours would miss the window where a gentle “have you checked?” actually helps. Our newborn threshold gives a full day’s earlier heads-up than that.

But tightening a single number for everyone doesn’t work either: in the first few days of life, a healthy baby’s output is still ramping up, so long dry gaps are genuinely normal, and a too-tight rule would cry wolf constantly. The honest answer isn’t one number — it’s a different number for each age band, each chosen to sit comfortably before any real concern while clearing the range of normal variation.

A note on the sources

We leaned hardest on the bodies that publish actual guidance: the WHO, the CDC, the AAP, and the NHS. One honest caveat: for the sleep rule there is no clinical standard at all — “overtiredness” is a comfort concept, not a safety one — so those numbers come from sleep-consensus sources, we graded them down accordingly, and we made that rule the gentlest of the three.

Every threshold is a default, and every default is adjustable per child. You know your baby better than a table does. Our job is to start you somewhere sensible — and to stay quiet the rest of the time.