Natural family planning · Catholic roots

Know your fertile window, naturally.

A gentle cycle journal for women who would rather not use hormonal contraception: Catholics living natural family planning, women of faith, and anyone who wants to know her body as it is. Notice two signs a day, mark your period, and see when pregnancy is more likely.

Coming soon to iPhoneNow in private beta How it works ↓

Private, on your iPhone
No account, no ads, no tracking
Made for NFP, never pushes contraception
English & Português

Fer, a small glowing companion in a leaf hood, waving

Today: cycle day, today's pregnancy chance, and one-tap logging — Today at a glance

Your cycles: the current cycle, averages, and every past cycle as a ring — Every cycle, side by side

A past cycle unfurled into a calendar of cycle days — Unfurl any cycle into a calendar

Choosing a mucus observation while Fer demonstrates it — Fer acts out each sign

Logging interest in intimacy, privately — Desire, tracked privately

Who Fer is for

For women who want to understand their fertility instead of switching it off.

Catholics living NFP

Fer was made with Catholic roots, for couples who live natural family planning and stay open to life, whether you are spacing pregnancies or hoping for one. Keep a clear chart to bring to your NFP instructor.

Women of faith

Whatever your tradition, Fer respects your conscience. It never suggests the pill, never judges, and leaves every decision to you and your spouse.

Hormone-free by choice

Can't take the pill, or would rather not? Fer helps you read your body's own signs, with no hormones, devices or account.

How Fer works

Fertility awareness, one small observation at a time. About thirty seconds a day.

Notice two signs

How it feels and what you see. Wetter, clearer signs mean you may be fertile. "Not observed" is always an option.

Mark your period

The first day starts each cycle. Fer keeps counting until you mark the end, and checks in with you each day.

See your window

Fer combines your signs, waking temperatures and cycle dates into one simple daily status, and shows its reasoning.

Period Possibly fertile Lower chance Blank means unknown, never “safe”

Made to journal everything

Fer keeps the whole story, and keeps it yours.

Fer shows you how

Pick a sign and Fer demonstrates it: drops, a splash, a stretchy strand. Learning your body shouldn't feel clinical.

Your cycles, side by side

Every past cycle as a ring. Open one and it unfurls into a calendar, with a day-by-day journal of everything you noted.

Desire & your cycle

Note when you're in the mood, and when you were intimate. Fer shows whether your desire follows your fertile days. Never used in estimates.

Private by design

No account, analytics or ads. Your journal lives on your iPhone. Apple Watch wrist temperature is shown beside it, only if you connect it.

Patterns, not guarantees

Fer can't confirm ovulation or mark any day as safe, and estimates can't rule out pregnancy. If you're avoiding pregnancy, learn a fertility awareness method with a qualified instructor and use Fer as your journal.