Sure, cosmetic plastic surgery done well can make you look younger; that’s why people do it, right?

But just how much younger can a patient expect to look after surgery? As much as nine years, according to research published online Monday afternoon in the journal Archives of Facial Plastic Surgery (one of the JAMA/Archives publications).

The authors — three plastic surgeons (and one a consultant for the pharmaceutical company Allergan Canada) — note that there’s been little data to help doctors tell patients exactly how much younger they’ll look after their procedures. That can lead to unrealistic expectations, the authors say.

To remedy that, the authors gathered before-and-after photos of 60 patients (54 of them female) ages 45 to 72 who’d agreed to allow their images to be used in scientific research. They asked a group of “raters” (medical school student volunteers) to gauge each subject’s age before and after surgery.

The raters were consistent in guessing patients’ before-surgery age at about 1.7 years younger than their actual, chronological age. They also consistently estimated patients’ post-surgery age at about a mean of 8.9 years younger than their actual age.

Overall, patients looked a mean of 7.2 years younger after surgery. But those results varied according to the procedures patients underwent. Those who had only face-lift and neck-lift looked a mean of 5.7 years younger than they actually were, and those who had those two procedures and work on their upper and lower eyelids looked 7.5 years younger than they were. Not surprisingly, those who went all out, having face- and neck-lift, eyelid work plus forehead-lift, were perceived as being 8.4 years younger than they were.

The authors explain that a big part of the plastic surgeon’s job is to manage patients’ expectations. Doctors typically can offer that patients will feel more attractive and look more refreshed after surgery; the new findings, the authors suggest, may allow them to confidently add looking younger to that list of likely outcomes.