Selling is really a timing question: every extra month you keep a car, it loses a little more value, but it also gives you more use. The best time to sell is when the value you would lose by waiting starts to outweigh the use you would get. Since the typical model loses around 32% over its first five years, most of that loss is concentrated early.
Understand the shape of the curve
Depreciation is not linear. It is steepest in the first years and flattens as a car ages, because a smaller and smaller share of value remains to be lost. That shape is why the “when to sell” answer differs for a nearly-new car and a ten-year-old one — and why checking your specific model's curve beats any rule of thumb.
Good moments to sell
Three windows tend to work in a seller's favor: before a depreciation cliff, where value is about to drop faster than usual; before an expensive scheduled service, when a big maintenance bill would cost more than it returns; and while demand for your body style is seasonally high — convertibles in spring, all-wheel-drive in autumn. If your car is still under warranty, selling before it expires can also help.
Check where your car actually sits
Rules of thumb only go so far. Open your model's page to see its year-by-year depreciation and typical prices by age, or estimate the value at a given mileage with the depreciation calculator. If the curve near your car's age is flattening, there is less urgency; if a steep drop is coming, selling sooner protects more of your money.
Sell it the way that keeps the most
How you sell matters as much as when. A private-party sale typically nets more than a trade-in, though a trade-in is faster and may lower your sales tax. Either way, clean service records and honest condition are what let you ask — and hold — a stronger price.