Two is nothing like one.
Tandem learns your twins' sleep separately — then tells you the one window where both of them can go down together.
Free during early access.
wren
1h 52m
otis
0h 34m
Both down together at 1:40 PM
the home screen, roughly
the problem
what the books say, and what the nights look like
“Put your baby down at the first sign of tiredness.”
They both showed you a sign. Twenty minutes apart. You have one pair of hands.
“Keep a consistent nap schedule.”
Their wake windows drift a little further apart every day. By Thursday nothing lines up, and you can't tell which one moved.
“Don't let your baby get overtired.”
One of them is overtired. The other one isn't tired yet. Pick.
Every tracking app on your phone was designed for one baby, then given a second profile. That is not the same problem. Schedule interdependence, doubled sleep debt, two children developing at different rates — these aren't more parenting. They're different parenting.
how it works
log it, and it does the math
01
log it
A sleep, a feed, a diaper. One tap, either kid. If you're mid-nurse with one arm free, that's the design constraint we built to.
02
it learns them
Tandem tracks each child's wake windows on their own curve and adapts as their patterns build. It'll say when it doesn't have enough nights yet, rather than guess.
03
it tells you when
Nap targets and bedtime for each of them — and the window where their two schedules actually overlap, so you get one break instead of none.
built for two
not one app with a second profile
The whole system assumes two children whose schedules affect each other. That assumption goes all the way down.
- Two separate models. Wren's wake windows are learned from Wren. Nothing is averaged across your twins — if one is going through a regression and the other isn't, you'll see exactly that.
- One timeline, both kids. Side by side, same axis. You can see the night one of them woke the other.
- The sync window. When their independent predictions are far enough apart to be a problem, Tandem solves for a single time that works for both — and never suggests one that leaves the younger-tired twin short.
- Both caregivers, same view. Invite a partner, a grandparent, a nanny. Everyone sees the same state.
shows its work
ask it at 3 AM, and check where the answer came from
There's an AI consultant inside Tandem that already knows both your kids' history. It cites what it's drawing on, every time, and it says “I don't know” when it doesn't.
Otis has been fighting his second nap for four days. Wren's still going down fine. What's happening?
Otis's afternoon wake window has stretched about 25 minutes over those four days — Wren's hasn't moved. That's usually the second nap getting squeezed as one twin's window lengthens ahead of the other's, not a regression.
Try pushing Otis's second nap 20 minutes later tomorrow and leaving Wren where she is. If he settles inside 15 minutes, that was it.
2 sources- Mindell & Owens — A Clinical Guide to Pediatric Sleep
- American Academy of Pediatrics — infant sleep guidance
illustrative — real answers cite your kids' own logged history
Answers are grounded in a corpus of 500+ clinical and research sources — pediatric sleep literature, AAP guidance, peer-reviewed papers. Not a model's vibes about babies.
built for 3 AM
designed not to wake you up further
The person using this is holding a baby in a dark room and has slept four hours. That's the design target, not an edge case.
dark by default
Near-black backgrounds and warm white text rather than pure white — a lower colour temperature at the same brightness. Readable at your phone's minimum brightness setting.
one answer, not three options
Sleep deprivation shrinks working memory. You get a recommendation and the reason for it, not a decision tree to work through at 3 AM.
no spinners, no cheerleading
Skeleton screens instead of loading messages. No exclamation marks, no “you're doing amazing.” You're doing a hard thing and you need information.
thirty seconds, one thumb
Logging is the thing you'll do most and the thing you'll least want to do. Everything else is built around keeping it fast.
wherever you are
works in the nursery with no signal
Tandem stores everything on your device first. Log a nap in a basement bedroom with one bar — it saves immediately and syncs the moment you're back. Your partner sees it seconds later.
There's nothing to download. Open it in your browser and add it to your home screen in two taps; it opens full-screen like any other app. Native iOS and Android apps are coming.
questions
the things people ask first
Is it free?
Yes, during early access. There's no card and no trial timer. We'll charge for it eventually — when we do, you'll hear about it well before anything changes.
Is there an app to download?
Not in the App Store yet. Tandem runs in your browser and installs to your home screen in two taps, where it behaves like any other app — full screen, works offline. Native iOS and Android apps are coming.
Do I have to log everything?
No. Sleep is what drives the predictions, so that's the one worth being consistent about. Feeds, diapers and the rest are there when you want them. Expect a few nights of data before the wake-window predictions are worth trusting — Tandem will tell you when it's still working it out rather than guessing at you.
Is this medical advice?
No. Tandem is not a medical device and it isn't a replacement for your pediatrician. It'll tell you when something belongs in a doctor's hands rather than trying to answer it.
Can my partner or our nanny use it too?
Yes. From settings you can create an invite code for another caregiver; they join your household and see the same live state on their own phone.
What ages does it cover?
From birth through the toddler years. If your twins were early, Tandem uses corrected age for its developmental phases — which matters a lot in the first year, and which most trackers get wrong.
What happens to our data?
We don't sell it. There's no ad network in Tandem and there never will be. You can export everything or delete your household outright from settings, and deletion means deletion.
who made this
it started as a dad trying to get two babies on the same schedule
It worked. They were sleeping through the night at two and a half months corrected. What began as a spreadsheet and a lot of reading turned into this — a system that reads the research so you don't have to, and applies it to your two specific kids.
we're early, and we'd rather say so
No million-download badge. No press logos. No wall of five-star reviews, because there aren't enough of us yet to have one. Here's what there is instead: a corpus of real clinical literature behind every answer, predictions that get measured against what actually happened, and a product that runs every night on a real set of twins. If we don't know something, the app says so — that's a deliberate choice, and it's the part we'd want you to hold us to.
get started
Free during early access. Takes about a minute, and you can log your first sleep straight away.