Natural Cycles
Natural Cycles is the first and only FDA-cleared app for use as birth control. You take your temperature every morning, the algorithm identifies your fertile days, and tells you whether to use protection. 93% typical use, 98% perfect use effectiveness. Three modes: Birth Control, Plan a Pregnancy, and Follow Pregnancy. Annual plan $119.99/yr includes a thermometer. Also works with Oura Ring and Apple Watch for overnight temperature. Not cheap, but cheaper than most contraception over time.
This is not a period tracker that also shows fertile days. Natural Cycles is FDA-cleared contraception. That's a meaningful regulatory distinction - it went through clinical trials, submitted safety data, and got cleared as a medical device for preventing pregnancy.
How it works: take your basal body temperature every morning before getting up (oral thermometer, or overnight via Oura Ring, Apple Watch, or the NC Band wearable). The algorithm analyzes temperature patterns to determine your fertile window. Green days = not fertile, use no protection. Red days = possibly fertile, use protection or abstain.
Effectiveness: 93% with typical use, 98% with perfect use. Comparable to the pill's typical-use rate. Not as effective as an IUD. Important to understand what "typical use" means - it accounts for human error (forgetting to take temperature, having unprotected sex on red days anyway).
Three modes: Birth Control (prevent pregnancy), Plan a Pregnancy (optimize timing for conception), and Follow Pregnancy (track your pregnancy once confirmed). The conception mode is solid - basically doing what Fertility Friend does with BBT but with a much nicer interface.
Annual plan: $119.99/yr with a thermometer included free. Monthly: $16.99/mo, thermometer sold separately for $39.99. FSA/HSA eligible.
Compared to Fertility Friend ($25-$45/yr), Natural Cycles is 3-5x the price but has a modern UI, FDA clearance, and wearable integration. FF is more powerful for charting obsessives. Natural Cycles is more practical for daily use.
Compared to Clue's Birth Control feature ($39.99/yr), Natural Cycles uses actual temperature data rather than cycle-history prediction, which is more biologically accurate.
The catch: you need to be consistent. If you hate morning routines or have irregular sleep schedules, the temperature readings will be unreliable. And on red days, you still need backup contraception. It's not effort-free.
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