What is a lab-grown diamond actually worth on resale?

Far less than you paid, and the honest answer is that nobody should buy one as a store of value. Lab-grown stones are real diamonds, graded by the same laboratories, but production capacity has grown quickly and retail prices have fallen steadily — which means the stone you buy today competes with cheaper new supply tomorrow. Secondary-market demand is thin, and many buyers of pre-owned jewelry price a lab-grown centre stone at close to nothing, valuing the setting metal instead. For most of the brands we cover we have found no published resale data at all, and we will not estimate a recovery rate we cannot source. Treat a lab-grown purchase as consumption: judge it on cost per wear, not on what it might fetch later.