Adding a single 8GB stick vs buying a new 16GB kit: Single stick saves half the cost and usually works fine

Adding a matching 8GB stick costs $12-18 vs $25-35 for a new 2x8GB kit, so you save roughly half. Compatibility is rarely an issue if speeds and timings match—modern boards just downclock if there’s a mismatch. Worst case, it doesn’t POST and you return it. Only buy a full kit if you’re building from scratch or need guaranteed dual-channel for overclocking.