Use our Combined Contraceptive Effectiveness Calculator below to see how pairing two birth control methods can boost your protection level. Input your chosen methods and whether you use them perfectly or typically to instantly view your enhanced effectiveness percentage.
Combined Methods Calculator
Understanding Typical Use vs. Perfect Use
Perfect use measures how effective a contraceptive method is when used consistently and correctly every time, typically in clinical trials. Typical use reflects how the method performs in real-life situations, where mistakes can happen, like a condom breaking, or forgetting to take a pill every now and then.
For example, birth control pills are 99% effective with perfect use, meaning only 1 out of 100 women may become pregnant each year. However, with typical use, their effectiveness drops to about 91%, resulting in 9 out of 100 pregnancies.
In contrast, long-acting methods like the hormonal implant have similar effectiveness rates for both perfect and typical use because they require little to no user intervention once in place. On the other hand, methods such as fertility awareness have a wider gap between perfect and typical use effectiveness due to the higher potential for user error.
Since everyday use often involves inconsistencies, it’s important to consider typical use rates when choosing a contraceptive method. Proper education and consistent application can help you achieve effectiveness closer to perfect use.
Are you looking for near–100% pregnancy prevention? Doubling up on contraceptive methods may be your best bet. Below, we’ll break down the benefits of using two forms of birth control at the same time, show you how to calculate their combined effectiveness, and help you understand important considerations when choosing the right contraceptive methods for your body and lifestyle.
Why Use Two Contraception Methods?
No single contraceptive method is 100% effective at preventing pregnancy. However, combining two can significantly reduce your overall risk. Common user errors—like missing a pill or incorrectly applying a patch—can happen even with highly effective birth control options. By using two methods simultaneously (e.g., a hormonal method plus a barrier method), you can compensate for these potential slip-ups and further lower your chance of unintended pregnancy.
- Hormonal Contraceptives (pills, patches, implants) can be very reliable if used correctly.
- Secondary Methods (condoms, spermicides, diaphragms) offer a backup layer of protection and can prevent certain STIs.
- Combined Use nearly closes any effectiveness gaps caused by human error or occasional misuse.
Check Your Specific Chance of Pregnancy
Our Advanced Contraceptive Risk Calculator can give even more accurate percentage odds of pregnancy with the help of peer-reviewed science.
Advanced Contraceptive Risk Calculator
How to Use
Simply enter the optional information and press the “Calculate” button. The more information you enter, the more accurate the results will be. Don’t worry, we don’t store your data.
This calculator is designed to estimate pregnancy odds over a real or hypothetical period of time.
Contraceptive Method: Simply select a methods from the drop down menu; if you don’t/didn’t use contraceptives, leave as “No Contraceptive”.
Did you use this method perfectly: During the period of time, did you use this method perfectly? Or did you, for example, forget to take a pill, or have a condom break?
Intercourse Times: During the period of time, how many times did you have intercourse? (e.g. 50)
Female Age: During the period of time, what was the age of the female participant? (e.g. 37)
Male Age: What is the male participant’s age? (e.g. 39)
Female Height: What is the female participant’s height? (e.g. 60 in)
Female Weight: What is the female participant’s weight? (e.g. 180 lb)
Work Hours per Week: How many hours do you work per week? (e.g. 25)
Daily Cigarettes: How many cigarettes do you smoke per day on average? (e.g. 5)
Weekly Alcohol Intake: How many standard alcoholic drinks do you drink per week? (e.g. 3)
The Math Behind Combined Effectiveness
When you combine two methods, you’re focusing on failure rates (the likelihood each method may fail). The chance that both methods fail at the same time is much lower.
- Convert Effectiveness to Failure Rate
- A method that’s 95% effective has a 5% (0.05) failure rate.
- A method that’s 90% effective has a 10% (0.10) failure rate.
- Multiply Failure Rates
- 0.05 (Method A’s failure) × 0.10 (Method B’s failure) = 0.005 (0.5%).
- Get Combined Effectiveness
- 1 − 0.005 = 0.995 (or 99.5% effective).
By using two birth control methods, you can approach a combined effectiveness near 99% or higher, depending on the methods and how consistently you use them.
Important Considerations for Doubling Up
While combining methods can drastically reduce pregnancy risk, you need to ensure compatibility:
Consult a Healthcare Professional: Each body is unique, so professional guidance helps you pick methods that work best together and with your health profile.
Avoid Interactions: For instance, certain lubricants might weaken condoms, or certain medications might reduce the effectiveness of hormonal methods.
Lifestyle Factors: If you have trouble remembering daily pills, adding a condom or another barrier could be a simpler, more consistent backup.
Final Thoughts
By understanding how combined effectiveness works, you can make more confident choices about your reproductive health. Whether you’re pairing hormonal methods (such as the pill, patch, or ring) with barrier methods (like condoms or spermicides), you’ll benefit from the extra insurance against unintended pregnancy.
Remember: Consistent and correct usage is key to maximizing any method’s effectiveness, single or combined.
Disclaimer
This information is intended for educational purposes and does not replace professional medical advice. Always consult a qualified healthcare provider for personalized guidance on birth control options.