The answer to 'when to replace bathtub' is that you should typically replace your bathtub every 10-15 years, or sooner if it shows signs of significant wear and tear. Bathtubs can last a long time with proper care and maintenance, but over time they can become cracked, chipped, or stained, and the finish may start to wear off.
Some common signs that it's time to replace your bathtub include cracks or chips in the surface, peeling or discolored finish, and difficulty keeping the tub clean and sanitary. If your bathtub is outdated or no longer fits your style preferences, that can also be a good reason to consider replacement. Replacing an old bathtub can also be a good opportunity to upgrade to a newer, more modern model with features like built-in shelves, grab bars, or jetted tubs.