In an era when everyone seems to be tracking their daily 10,000 steps with a Fitbit, measuring calories with MyFitnessPal and monitoring fertility with apps like Glow, it's easy to get hung up on numbers. Is my body mass index sitting nicely below 25? Is my blood pressure normal for my age? Is my blood level of that nasty LDL cholesterol in check—say, below 100 mg/dL? But this health-by-the-numbers approach has its limits and might even lead you astray. Newer research suggests we should embrace more personalized goals instead of one-size-fits-all targets.

Take blood sugar—an issue for the roughly half of American adults who either have diabetes or are prediabetic. For decades doctors have told such patients to aim below one specific target: a 7 percent blood level of hemoglobin A 1C —a sugar-coated protein that reflects blood glucose levels for the previous two to three months. The magic number was based on a classic 1993 study that showed multiple, long-term benefits to staying below seven—through diet, drugs or exercise, or all three.

JoAnn Manson has seen patients drive themselves crazy chasing the perfect seven during her 25 years in clinical practice and as chief of preventive medicine at Boston's Brigham and Women's Hospital. That goal tends to grow more elusive over time as the body's insulin production drops, leading patients to pile on the medications. Side effects multiply. So do the medical bills. And, crucially, newer research shows that not all drugs that lower A 1C levels are equally good at protecting diabetics from heart disease, kidney failure, blindness and other dreaded complications.

Increasingly, experts are recommending a more individualized approach to managing the disease. One consideration is that the benefits of “tight control” over blood sugar accrue slowly over many years, whereas the harms of overtreatment—such as a drop in glucose that can make you pass out—happen fast. That means “an older or frailer patient might not live long enough to see the benefits,” says endocrinologist Judith Fradkin of the National Institute of Diabetes and Digestive and Kidney Diseases. Such a patient might be more concerned about breaking bones if he or she falls because of low blood sugar. Bottom line: treatment becomes a discussion.

The same may be said for managing cholesterol levels. Fifteen years ago doctors told patients they should keep their LDL cholesterol below 100 mg/dL and, if they had already had a heart attack or stroke, aim for 70 mg/dL, with help from diet, exercise and statin drugs. Although these ideas linger, the guidelines changed in 2013 after a panel of experts found insufficient evidence for such specific goals and replaced them with a more individualized approach. “We took a big step toward getting people to think about what kind of risk group they were in, as opposed to saying that below some number, your risk disappears and that above the number, all the risk is present,” says cardiologist Neil J. Stone of Northwestern University, who chaired the panel.

That panel's report concluded that there was good evidence for using statins—along with lifestyle changes—to lower cholesterol in high-risk patients, such as those with a history of heart attack or stroke or people between ages 40 and 75 with diabetes. But for the “worried well,” a careful assessment and decision making together with the patient was the best way to go. The panel published a risk-estimation tool to guide the conversation.

Mind you, there are still some bright lines. An LDL level above 190 mg/dL should be treated, no matter what. And a hemoglobin A 1C count at nine or above means danger for anyone. But overall, medicine has embraced the mantra of shared decision making. One reason is a greater understanding of the harms of both undertreating and overtreating. Another is respect for patient preferences. “People tend to know themselves pretty well,” Manson says. Some are sensitive to drug side effects; some are terrified by a family history of heart attacks or strokes.

Third, there is growing recognition that the perfect must not become the enemy of the good. Take body weight: in one major study, prediabetic adults, many of them obese, halved their risk of developing diabetes over the next three years just by dropping an average of 15 pounds—still far from a svelte ideal.

Personalized goals and shared decision making put a greater burden on all of us to be informed. Luckily, this is one way those health-related apps can help. Fradkin, Manson and others are excited about a new generation of truly smart apps that are less about counting and more about guiding healthy decisions.