Rule for neuter · das
-chen → das, always neuter, no exceptions.
The suffix -chen turns any noun into a diminutive - and no matter what gender the original word had, the result is always neuter (das). The best-known example is das Mädchen ("girl"): even though it refers to a female person, the word is neuter because the grammatical rule overrides natural gender. Other everyday examples are das Schnäppchen (a bargain) and das Brötchen (bread roll). It's a rare pattern among the 2,400 most frequent words - only a handful qualify - but it has zero exceptions, so you can rely on it every time you see a word ending in -chen.