Objective To assess preconception lifestyle behaviours between individuals actively trying to conceive (TTC) and planning for future pregnancies (PFF). Design Retrospective cross-sectional study. Setting UK-based women. Population 235,311 women who completed an online reproductive health questionnaire between September 2020 and November 2024. Methods Self-reported data on reproductive intent as well as smoking, vaping, alcohol, and drug use were analysed. Logistic regression models adjusted for age, BMI, and lifestyle factors compared behavioural differences between TTC and PFF groups. Main Outcome Measures Prevalence of modifiable lifestyle factors (smoking, vaping, alcohol, and drug use) in TTC vs. PFF groups, stratified by age and TTC duration. Results TTC individuals smoked more than PFF individuals (9.1% vs. 7.3%; aOR = 1.76, 95% CI: 1.68–1.84, p < 0.001). Although vaping was more prevalent among PFF individuals (13.7% vs. 12.3%), TTC individuals had higher adjusted odds of vaping (aOR = 1.14, 95% CI: 1.10–1.18, p < 0.001). TTC individuals were more likely to abstain from alcohol (48.8% vs. 30.5%, p <0.001), however, many still exceeded the UK’s recommended low-risk limit of 14 units per week. Smoking, vaping, and drug use were highest in those under 25, while alcohol use peaked in those over 35. Smoking and vaping rates were significantly higher among those TTC for >12 months. Conclusions Findings show continued engagement in high-risk behaviours despite TTC, underscoring the need for targeted interventions, particularly vaping cessation and age-specific counselling, to mitigate risks earlier in the reproductive timeline and improve fertility outcomes.