Adding a mismatched stick will work, but you lose full dual-channel.

Yes, it will cause a dual-channel issue — but not a catastrophic one.

Your existing 2x8GB runs in full dual-channel. Add a single 16GB stick, and your motherboard will likely switch to “flex mode.” That means the first 16GB of the 32GB total will run dual-channel (the original 2x8 plus half of the new stick), and the remaining 8GB on the new stick will run single-channel.

For most games and daily use, the performance hit is small — like 3-5% in CPU-heavy tasks. You probably won’t notice it unless you’re benchmarking or doing memory-sensitive work. The rank difference (single vs dual) isn’t the main issue here; it’s the asymmetry.

If you want to keep full dual-channel, sell your old 2x8 kit and buy a 2x16GB kit. It’ll cost a little more but avoids the flex mode compromise. Otherwise, stick with what you have and don’t stress about it.

Future You won’t care about the 5%.