The standard advice is to take AB one year, BC the next. It feels responsible. It also costs you a full year you could spend on multivariable calculus, linear algebra, AP Statistics, or nothing at all.
Here's the actual decision framework: BC contains everything in AB plus series, parametric equations, and polar functions. If you can place into precalculus honors or above and you're comfortable with function behavior and algebra at speed, you can take BC directly. The extra BC topics are not dramatically harder than the AB topics — they're just more of the same style of thinking.
Colleges treat a 5 on BC the same whether you took AB first or not. The score report does include an AB subscore, which is calculated from the AB-equivalent portion of the BC exam. So skipping AB costs you nothing on paper and gains you a year.
The one case where taking both makes sense: your school offers BC in 11th or 12th grade only, and taking AB in 10th grade gets you there a year earlier than you otherwise would. That's a sequencing argument, not a difficulty argument.
The other case worth flagging: if precalculus felt like a grind rather than manageable work, BC in one shot will be stressful. AB first is a real option — just own that it's a pacing choice, not a prerequisite.
A practical test before committing to BC directly: work through a few BC free-response questions from a released exam. Not to get them right — to see whether the problem structure feels foreign or just unfamiliar. Foreign means slow down. Unfamiliar means you're probably ready.
A small tool in this space: StudyPebble — adaptive AP/SAT practice with AI grading.
Bottom line: if you're strong through precalc and your school allows it, take BC and skip AB. The year is worth more than the safety net.