Know Her vs
DuoSync

DuoSync makes you guess a number most men don't know, then charges you $9.99/month for the privilege of guessing wrong.

★  Nothing to guess, less to pay
Know Her period tracker app — home screen widget showing her cycle phase

Setting it up yourself doesn't help much if step one is a number you have to make up.

Credit where it's due: DuoSync doesn't require her account — you enter her period start date and average cycle length yourself, with her consent, and it runs from there. But most men don't actually know her average cycle length; you'd be entering a guess and letting the app treat it as fact, with no sign it ever corrects itself once it has one. Know Her only asks for the date her last period started — no number to invent — and self-calibrates from there, getting more accurate the longer you use it instead of staying wrong in the same direction.

What each app actually asks you to know

Before you see a single thing, this has to happen first.

DuoSync

  • Her period start date — same as Know Her.
  • Her average cycle length — a number required upfront that most men don't know off the top of their head.
  • No sign it self-calibrates — the estimate appears to stay fixed rather than adjusting to her actual cycle.

You do the setup yourself — starting with a guess the app will treat as fact and never revisit.

Know Her

  • The date her last period started. That's it. No cycle-length guessing.

Starts with research-backed averages and self-calibrates every cycle — the longer you use it, the more accurate it gets.

Feature comparison

Know Her vs DuoSync, side by side.

Know Her DuoSync
Built for male partners ✓ Purpose-built ✓ Purpose-built
She needs no app or account ✓ Yes ✓ Yes
You need an account to log in ✓ No ✓ No — "no sign-up required" per its own site
No cycle-length question ✓ Only needs last period date ✗ Requires her average cycle length
Predictions self-calibrate ✓ Yes — learns her cycle ✗ No sign of self-calibration
100% offline (stored locally) ✓ Yes ✓ Yes, per its listing
Home screen widget ✓ Yes ✗ Not listed
Face ID / biometric lock ✓ Yes ✗ Not listed
Private notes on the calendar ✓ Yes — offline, only yours ✗ No
Your price $2.99/mo — 14-day free trial $9.99/mo or $29.99/yr

Design intent matters

What the app was built to solve changes everything about how it works.

Know Her

  • ✓ Only needs her last period date — no cycle-length guess
  • ✓ Self-calibrates to her specific cycle over time
  • ✓ Dashboard: energy, mood, tips in plain language
  • ✓ Widget: one-tap phase check from the home screen
  • ✓ Private notes and reminders on the calendar
  • ✓ Face ID lock for extra privacy

DuoSync

  • ✗ Needs her average cycle length upfront
  • ✗ No indication predictions improve over time
  • ✓ Anniversary/birthday reminders, custom date tracking
  • ✗ No home screen widget found
  • ✗ Costs more per month than Know Her

Price comparison

What it actually costs you.

Know Her Free to download — full access for 14 days

Then $19.99/year (or $2.99/month). Self-calibrates over time, home screen widget, Face ID lock, private notes.

DuoSync $29.99 per year — or $9.99/month

Costs more per month, and needs her average cycle length upfront with no sign of self-calibration.

At least $10 less per year, with fewer guesses required upfront.

Common questions

About choosing between Know Her and DuoSync.

No — DuoSync is designed for you to set up on your own, entering her period start date and average cycle length yourself (with her consent). She doesn't need the app or an account. Know Her works the same way in that respect, but skips the average cycle length question entirely — you only need the date her last period started.
There's no indication that it does. DuoSync calculates from the average cycle length you enter, but nothing suggests that estimate adjusts as her actual cycles come in. Know Her self-calibrates — every confirmed period makes its predictions more accurate to her specific rhythm.
DuoSync's premium subscription runs $9.99/month or $29.99/year. Know Her is free to download, with a 14-day trial that includes full access, then just $2.99/month or $19.99/year — noticeably less for a subscription that also self-calibrates and doesn't require guessing her cycle length upfront.
Yes. Know Her stores everything on your device — no account, no cloud, no sync. All data stays on your phone. You can lock it with Face ID or biometrics for extra privacy.
No. Know Her works entirely from information you enter yourself — no account for her, nothing to install, nothing to share. You just need the date her last period started. She doesn't even need to know you're using it.
Yes. Everything stays on your phone — no account, no cloud, no sync, nothing to leak. You can lock the app with Face ID or biometrics for extra privacy on top of that.
You get 14 days of full access, completely free. After that, Know Her runs on a simple subscription — monthly or annual. Cancel anytime directly in your App Store settings.
No. Know Her is designed to help you understand and plan around her cycle — it's not a medical device, diagnostic tool, or method of contraception. For health decisions, always consult a healthcare professional.

More comparisons

See how Know Her stacks up against other apps.

Know Her vs Flo for Partners Know Her vs Clue Connect Know Her vs Stardust Know Her vs Selin Know Her vs Maya Know Her vs Yuni Know Her vs Phases Know Her vs GF Tracker Know Her vs Mayday

Available on
iOS & Android.

Free for 14 days.

No commitment. Cancel anytime.

Download on the App Store
Get it on Google Play