Breast Cancer Risk Calculator — 5-Year Risk Estimate (Gail Model)
Estimate your personal 5-year breast cancer risk based on the published Gail model risk factors: your age, age at first period, age at first live birth, number of first-degree relatives with breast cancer, and biopsy history.
years
Age at first menstrual period
Age at first live birth (or no children)
First-degree relatives with breast cancer
Previous breast biopsies
Atypical hyperplasia found on any biopsy
Estimated probability of developing invasive breast cancer in the next 5 years
- 1
Age-matched baseline 5-year risk
1.43 %Published 5-year incidence rate for this age group (Costantino 1999) - 2
Combined relative risk
1.1×Product of relative risks for menarche age, family history, prior biopsies, and atypical hyperplasia - 3
5-year breast cancer risk
1.43 % × 1.1 = 1.6 %
How does this calculator work?
Multiply an age-specific baseline 5-year risk (0.2%–3.1%, from SEER data) by relative risk factors for menarche age, family history and first-birth timing, prior biopsies, and atypical hyperplasia. A result ≥ 1.67% meets the US threshold for elevated risk. Based on the published Gail model (Costantino 1999); not validated for BRCA carriers.
Formula
How this is calculated
The Gail model (Gail et al. 1989, refined by Costantino et al. 1999) estimates absolute breast cancer risk by combining a population baseline — the age-specific incidence rate for women with average risk factors — with a set of multiplicative relative risks derived from the Breast Cancer Detection Demonstration Project (BCDDP) cohort. The published baseline 5-year risks range from about 0.20% at age 20–24 to about 2.9% at age 70–74 for non-Hispanic white women.
Relative risk factors used here: age at menarche (< 12 years raises risk by 21%); number of first-degree relatives with breast cancer combined with age at first live birth (an interaction term reflecting that delayed first pregnancy and a positive family history act synergistically); number of prior breast biopsies (each biopsy multiplies risk by ~1.7); and whether any biopsy found atypical ductal or lobular hyperplasia (an additional 1.82× multiplier when true).
This calculator uses published Gail model values for non-Hispanic white women. Risk estimates differ for Black, Hispanic, Asian and other populations (the National Cancer Institute provides race-specific models at bcrisktool.cancer.gov). The model does not include BRCA1/2 status, dense breasts, hormone use or other known risk factors. A 5-year risk ≥ 1.67% qualifies women aged ≥ 35 for preventive chemoprophylaxis under US guidelines — discuss any elevated result with your clinician.
Frequently asked questions
1.67% is the US regulatory threshold used since the NSABP P-1 trial: women at or above this level are considered at "increased risk" and may be candidates for preventive therapy such as tamoxifen or raloxifene. It means that in a group of 1,000 women with similar risk profiles, about 17 would develop invasive breast cancer over 5 years.
No. The Gail model was derived from a population without BRCA testing and substantially underestimates risk for BRCA1/2 carriers. Women with a strong family history (multiple affected relatives, ovarian cancer in the family, male breast cancer) should be referred for genetic counselling rather than relying on the Gail model alone.
Mammography guidelines (USPSTF, ACS, ACR) are primarily based on age, not Gail model score. However, women with elevated risk may be offered additional screening such as annual MRI alongside mammography. This calculator is an educational starting point — your clinician will consider many additional factors when advising on screening.
TG we-Calculate Editorial Team. (2026). Breast Cancer Risk Calculator — 5-Year Risk Estimate (Gail Model) [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/breast-cancer-risk-calculator
TG we-Calculate Editorial Team. "Breast Cancer Risk Calculator — 5-Year Risk Estimate (Gail Model)." TG we-Calculate. 2026. https://we-calculate.com/calculator/breast-cancer-risk-calculator.
TG we-Calculate Editorial Team, "Breast Cancer Risk Calculator — 5-Year Risk Estimate (Gail Model)," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/breast-cancer-risk-calculator
@misc{wecalculate_breast_cancer_risk_calculator, title = {Breast Cancer Risk Calculator — 5-Year Risk Estimate (Gail Model)}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/breast-cancer-risk-calculator}}, year = {2026}, note = {TG we-Calculate} }
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