Circle's revenue is almost entirely interest on the dollars backing USDC. Every USDC in circulation is matched by a dollar held in short-term US government debt, Circle keeps most of what that dollar earns, and that line is 94 percent of what the company makes. Both inputs are public: how much USDC exists is published every day, and the Circle Reserve Fund publishes the rate the reserves earn. Multiplying them has landed within 0.6 percent of every quarter Circle has filed since the first quarter of 2024.

That balance is now shrinking. USDC peaked at $79.2B on 17 March 2026 and stands at $71.8B, down 9.4 percent. Supply fell $3.6B inside the June quarter and another $1.3B since 30 June, which puts the September quarter on course for $638M to $642M of reserve interest against $667M in June. Thirty-five of that quarter's 92 days are already measured, so the figure reads closer to a measurement than a forecast.

The decline is not evenly shared. Stablecoin supply fell $4.4B between 31 March and 30 June, USDC accounted for $3.6B of that fall, and USDT grew $0.4B over the same window. USDC's share of all stablecoins slipped to 23.9 percent from 24.8. Trading is the largest use of both tokens, at 49.6 percent of USDC end-user volume against 48.2 percent of USDT, and what differs is scale: USDT moved $1,308B in the first half of 2026 against USDC's $159B. Most stablecoin payment activity runs on Tron, where USDT holds $89.5B against USDC's $28M. USDC has payment users, but too few to hold the balance up when trading slows.

One input is moving in Circle's favour. Kalshi prices a September rate cut at 3 percent against 50 percent for a rise, and Polymarket US puts a rise somewhere in 2026 at 68 percent. A rise of 0.25 percent adds about $44M a quarter at the current balance. The catch is that higher rates also cool the risk appetite that brings USDC onto exchanges, so the move that lifts the yield can shrink the balance.

Circle's own tokenized US Treasury fund pays it less per dollar than USDC does. USYC has grown to $3.0B, about a fifth of a $15B market that has grown 7.6 times in two years. Circle keeps about 2 percent on a USDC dollar before distribution to partners other than Coinbase, against about 0.37 percent on a USYC dollar, so every dollar that moves across pays it four to five times less. Institutions hold nearly all of these funds today. As DeFi protocols accept them as collateral and retail platforms list them, they could become a serious alternative for the non-payment uses that make up most stablecoin volume.

Informational only. Not investment advice.