Do unused Helixes carry over to the next month? Locked

It depends where the Helixes came from. Monthly Helixes from your subscription do not roll over: at the start of each billing cycle your subscription Helix balance is refilled to your tier's amount, and anything unused from the previous month is cleared. Helixes from Helix packs bought separately never expire and stay in your wallet for as long as you need them. When you unlock a chapter, your monthly subscription Helixes are always spent first, so any Helixes you bought separately are preserved as long as possible.