Understand her cycle.
Be a better partner.
Four Phases is a cycle tracking app for men. Put in her last period date and cycle length, and from then on it tells you which phase she is in today and what to do about it.
This is what a morning looks like.
A real brief, exactly as the coach wrote it for the fourth day of the follicular phase. Six lines, one of them a message you can send as is.
Today's brief
Suggest something she's never tried before.
Her energy is climbing and she's wired for novelty right now.
A new trail, a weird cuisine, a spontaneous weeknight plan.
Don't meet her enthusiasm with "I don't care, you pick."
Dark chocolate and berries. Rising estrogen loves the antioxidants.
Send her this
I just found this place we haven't been to. You free Thursday?
Four phases, every month.
Each one asks something different of you. The strip is the one from the app.
Running on empty. Take things off her plate before she asks.
Energy and ideas coming back. Keep up with her.
The week to plan the date, and to put the phone away on it.
Where most guys lose. Agree with her before you fix anything.
How it works
Set it up once. Check it every morning.
01
Two numbers
Her last period and her average cycle length. If she wants in, invite her and her own dates replace your estimate.
02
A brief each morning
Which phase, which day, how she is likely feeling, and one thing worth doing about it.
03
A coach when you need one
Ask about a gift, a dinner, or what to say after an argument. It already knows what phase she is in.
Built for his phone, not hers.
Today
Phase, day, and how long until the next shift. Tap the symptoms she mentioned and the brief accounts for them.
Calendar
Every day coloured by phase, so you book the trip, or the hard conversation, on a good week.
Phase guides
What is going on in her body, what tends to help, what tends to backfire. Read once, come back when you forget.
Read the guidesWhy this exists
Nobody needs a textbook on this. You need to know what to do today.
Period trackers are built for the person having the period. This one is for the guy next to her, who wants to understand what is going on and does not want to make it weird. It reads the way a friend who happened to know this stuff would explain it, and it stays practical: what to cook, what to plan, when to leave a subject alone.
Most of being a good partner is timing. This tells you when.
Privacy
Her health data is nobody's business. Including ours.
Cycle data gets subpoenaed, sold and leaked elsewhere in this industry. Here it sits in your own account, readable by you and the partner you link. That is the whole list.
Her name never reaches the AI
The app strips it before any request to the coach goes out. It is saved in your account so your devices stay in sync, never sold or shared.
Only you two can read it
The database limits every row to you and your linked partner. We cannot casually browse it either.
Delete it yourself
From Settings, the data or the whole account. You never have to email anyone to leave.
No ads, no brokers
No tracking SDK in the app and no data for sale. That is not how this makes money.
Does she need to use the app too?+
No. Her last period date and average cycle length are enough to predict the rest. If she wants in, invite her from Settings and her real dates replace your estimate.
Is it free?+
Your first week is free, with everything turned on. After that, Four Phases Pro is $9.00 a month or $89.99 a year, bought in the iPhone app and billed by Apple. You need an account either way, because it links you to her and keeps your setup when you change phones.
Is there an iPhone app?+
Yes. Four Phases runs on iPhone and in any browser, and one account works in both. The web version is the same app.
Is this medical advice?+
No. It is coaching for partners. Cramps that worry you, irregular cycles, anything that seems off: that is a clinician's job, not ours.
Where does her data live?+
In your own account on our database, which only lets you and the partner you link read it. It is never sold or shared with advertisers, and you can delete all of it from Settings.
How does the coach work?+
The daily brief and the chat run on Anthropic's Claude. A request carries the cycle phase, the day number, any symptoms you logged, and your question, and never her name. Your chat history stays in your account so it follows you between devices.
Be the partner she didn't know she had.
Setup takes about thirty seconds and costs nothing.