diff --git a/src/app/api/fee-compare/route.ts b/src/app/api/fee-compare/route.ts
index 7572fdf1b..c7ffe03c3 100644
--- a/src/app/api/fee-compare/route.ts
+++ b/src/app/api/fee-compare/route.ts
@@ -37,12 +37,14 @@ const EVM_WALLET_VENUES = new Set(["hyperliquid", "gains", "gmx-v2"]);
 // Rate caches
 // ──────────────────────────────────────────────────────────────────────
 
-// Gains v6 borrowingRatePerSecondP and lastFundingRatePerSecondP use 1e18 precision
-const GAINS_CARRY_PRECISION = 1e18;
+// Gains v6 borrowingRatePerSecondP uses 1e18; lastFundingRatePerSecondP uses 1e21
+const GAINS_BORROW_PRECISION = 1e18;
+const GAINS_FUNDING_PRECISION = 1e21;
 // Fallback when API doesn't expose per-pair data (~0.04%/day expressed per-second)
 const GAINS_BORROW_DEFAULT_PER_SEC = 0.0004 / 86400;
-// USDC collateral index on Arbitrum (same as collateralIndex filter in fetchGainsTrades)
-const GAINS_USDC_COLLATERAL_IDX = 3;
+// USDC is array[2] in vars.collaterals (0-indexed); its collateralIndex field = 3 (1-indexed).
+// The collateralIndex===3 filter in fetchGainsTrades refers to the field value, not the array position.
+const GAINS_USDC_COLLATERAL_IDX = 2;
 
 let gainsFeeCache: {
   coinRoundTrip: Record<string, number>;
@@ -145,6 +147,7 @@ type GainsWalletData = {
   events: number;
   feesUsdc: number;
   fundingFeesUsdc: number;
+  fundingEstimated: boolean;
   borrowingFeesUsdc: number;
   netCostUsdc: number;
   positionSizeUsdc: number;
@@ -283,13 +286,13 @@ async function fetchGainsFeeRates(): Promise<{
     // Borrow rate per second (v2 takes precedence over legacy)
     const v2Borrow = v2BorrowParams[i]?.borrowingRatePerSecondP;
     if (v2Borrow) {
-      borrowPerSecPerCoin[p.from] = parseFloat(v2Borrow) / GAINS_CARRY_PRECISION;
+      borrowPerSecPerCoin[p.from] = parseFloat(v2Borrow) / GAINS_BORROW_PRECISION;
     }
 
     // Funding rate per second (absolute value — longs and shorts may face same magnitude)
     const fundingRate = fundingPairData[i]?.lastFundingRatePerSecondP;
     if (fundingRate) {
-      fundingPerSecPerCoin[p.from] = Math.abs(parseFloat(fundingRate)) / GAINS_CARRY_PRECISION;
+      fundingPerSecPerCoin[p.from] = Math.abs(parseFloat(fundingRate)) / GAINS_FUNDING_PRECISION;
     }
   }
 
@@ -1046,11 +1049,24 @@ export async function GET(req: Request) {
           }
         }
 
+        // When the API doesn't return per-trade funding (meta absent or zero), fall back to
+        // the same per-second rate estimation used in the crossSim projection.
+        let fundingEstimated = false;
+        if (fundingFeesUsdc < 0.01 && Object.keys(gainsData.fundingPerSecPerCoin).length > 0) {
+          const gainsPositions = reconstructGainsPositions(usdcTrades, cutoffMs);
+          const est = estimateGainsFundingFees(gainsPositions, gainsData.fundingPerSecPerCoin);
+          if (est > 0.01) {
+            fundingFeesUsdc = est;
+            fundingEstimated = true;
+          }
+        }
+
         const netCostUsdc = feesUsdc + fundingFeesUsdc + borrowingFeesUsdc;
         walletData = {
           events: usdcTrades.length,
           feesUsdc,
           fundingFeesUsdc,
+          fundingEstimated,
           borrowingFeesUsdc,
           netCostUsdc,
           positionSizeUsdc: notionalUsd,
diff --git a/src/components/fee-compare-client.tsx b/src/components/fee-compare-client.tsx
index c2434193b..a98e7b838 100644
--- a/src/components/fee-compare-client.tsx
+++ b/src/components/fee-compare-client.tsx
@@ -76,6 +76,7 @@ type GainsWalletData = {
   events: number;
   feesUsdc: number;
   fundingFeesUsdc: number;
+  fundingEstimated: boolean;
   borrowingFeesUsdc: number;
   netCostUsdc: number;
   positionSizeUsdc: number;
@@ -748,6 +749,9 @@ function WalletSide({
                 <div className="flex items-center justify-between">
                   <p className="text-[11px] text-ink-faint">
                     Funding {gW.fundingFeesUsdc > 0 ? "paid" : "received"}
+                    {gW.fundingEstimated && (
+                      <span className="ml-1 text-[9px] text-ink-faint/50 italic">est.</span>
+                    )}
                   </p>
                   <p className={`font-mono text-xs font-semibold ${gW.fundingFeesUsdc > 0 ? "text-red-400" : "text-emerald-500"}`}>
                     {gW.fundingFeesUsdc > 0