diff --git a/backend/src/api/controllers/yields.ts b/backend/src/api/controllers/yields.ts
index f62aa26..5a38dfa 100644
--- a/backend/src/api/controllers/yields.ts
+++ b/backend/src/api/controllers/yields.ts
@@ -1,7 +1,9 @@
 import type { Request, Response, NextFunction } from "express";
 import { YieldService } from "../../services/yield.js";
+import { NotificationService } from "../../services/notifications.js";
 
 const yieldService = new YieldService();
+const notificationService = new NotificationService();
 
 function formatYieldPerShare(yieldAmount: string, totalShares: string): string {
   const yieldBig = BigInt(yieldAmount);
@@ -86,6 +88,57 @@ export async function getEpochDetail(req: Request, res: Response, next: NextFunc
   }
 }
 
+// ── Epoch comparison (#820) ──────────────────────────────────────────────────
+export async function compareEpochs(req: Request, res: Response, next: NextFunction) {
+  try {
+    const contractId = String(req.params["contractId"]);
+    const epochA = Number(req.query.a);
+    const epochB = Number(req.query.b);
+
+    if (!Number.isInteger(epochA) || epochA <= 0 || !Number.isInteger(epochB) || epochB <= 0) {
+      res.status(400).json({ error: "BadRequest", message: "Both a and b must be positive integers" });
+      return;
+    }
+
+    const result = await yieldService.compareEpochs(contractId, epochA, epochB);
+    if (!result) {
+      res.status(404).json({ error: "NotFound", message: "One or both epochs not found" });
+      return;
+    }
+
+    res.json(result);
+  } catch (err) {
+    next(err);
+  }
+}
+
+// ── Next epoch projection (#821) ─────────────────────────────────────────────
+export async function getNextEpochProjection(req: Request, res: Response, next: NextFunction) {
+  try {
+    const contractId = String(req.params["contractId"]);
+    const projection = await yieldService.getNextEpochProjection(contractId);
+    res.json(projection);
+  } catch (err) {
+    next(err);
+  }
+}
+
+// ── Epoch closed webhook (#819) ──────────────────────────────────────────────
+export async function handleEpochClosed(
+  contractId: string,
+  epoch: number,
+): Promise<void> {
+  const result = await yieldService.closeEpochIfFullyClaimed(contractId, epoch);
+  if (result) {
+    await notificationService.notify("epoch.closed", {
+      contractId,
+      epoch,
+      yieldAmount: result.epochData.yieldAmount,
+      closedAt: result.epochData.closedAt,
+    });
+  }
+}
+
 export async function getUserPendingYield(req: Request, res: Response, next: NextFunction) {
   try {
     const result = await yieldService.getUserPendingYield(
diff --git a/backend/src/api/routes/yields.ts b/backend/src/api/routes/yields.ts
index 937de0d..f8c7b35 100644
--- a/backend/src/api/routes/yields.ts
+++ b/backend/src/api/routes/yields.ts
@@ -8,6 +8,8 @@ import {
   getYieldSummary,
   getYieldPerShareHistory,
   getYieldTimeline,
+  compareEpochs,
+  getNextEpochProjection,
 } from "../controllers/yields.js";
 import { getYieldsStream } from "../controllers/yields-stream.js";
 import { validateQuery, validateParams } from "../middleware/validate.js";
@@ -63,6 +65,17 @@ yieldsRouter.get(
   validateParams(epochDetailParamsSchema),
   getEpochDetail,
 );
+
+// ── Epoch comparison (#820) ──────────────────────────────────────────────────
+const epochCompareQuerySchema = z.object({
+  a: z.coerce.number().int().positive(),
+  b: z.coerce.number().int().positive(),
+});
+yieldsRouter.get("/:contractId/epochs/compare", validateQuery(epochCompareQuerySchema), compareEpochs);
+
+// ── Next epoch projection (#821) ─────────────────────────────────────────────
+yieldsRouter.get("/:contractId/next-epoch-projection", getNextEpochProjection);
+
 yieldsRouter.get("/:contractId/yield-per-share-history", validateQuery(yieldHistoryQuerySchema), getYieldPerShareHistory);
 yieldsRouter.get("/:contractId/pending/:userAddress", getUserPendingYield);
 
diff --git a/backend/src/db/migrations/030_epoch_closed_at.sql b/backend/src/db/migrations/030_epoch_closed_at.sql
new file mode 100644
index 0000000..931c1c8
--- /dev/null
+++ b/backend/src/db/migrations/030_epoch_closed_at.sql
@@ -0,0 +1,3 @@
+-- Add closed_at column to epochs for webhook idempotency (#819).
+-- closed_at is set exactly once when totalClaimed >= yieldAmount.
+ALTER TABLE epochs ADD COLUMN IF NOT EXISTS closed_at TIMESTAMPTZ;
diff --git a/backend/src/services/indexer.ts b/backend/src/services/indexer.ts
index 1da8bd9..e429b39 100644
--- a/backend/src/services/indexer.ts
+++ b/backend/src/services/indexer.ts
@@ -11,6 +11,7 @@ import {
 } from "./stellar.js";
 import { VaultService } from "./vault.js";
 import { UserService } from "./user.js";
+import { YieldService } from "./yield.js";
 import { NotificationService } from "./notifications.js";
 import { indexerEventsProcessedTotal, indexerLastLedger } from "./metrics.js";
 import { cacheDel } from "../cache/redis.js";
@@ -1010,6 +1011,24 @@ export class Indexer {
     );
     await cacheDel(`pending-yield:${contractId}:${userAddress}`);
     logger.info({ contractId, userAddress, epoch }, "Processed yield_claimed event");
+
+    // Check if epoch is now fully claimed and fire webhook (#819)
+    try {
+      const yieldService = new YieldService();
+      const result = await yieldService.closeEpochIfFullyClaimed(contractId, epoch);
+      if (result) {
+        const notificationService = new NotificationService();
+        await notificationService.notify("epoch.closed", {
+          contractId,
+          epoch,
+          yieldAmount: result.epochData.yieldAmount,
+          closedAt: result.epochData.closedAt,
+        });
+        logger.info({ contractId, epoch }, "Fired epoch.closed webhook");
+      }
+    } catch (err) {
+      logger.warn({ contractId, epoch, err }, "Failed to check epoch close after yield claim");
+    }
   }
 
   private async handleEarlyRedemptionProcessed(
diff --git a/backend/src/services/yield.ts b/backend/src/services/yield.ts
index bc8c985..a272f5a 100644
--- a/backend/src/services/yield.ts
+++ b/backend/src/services/yield.ts
@@ -98,8 +98,9 @@ export class YieldService {
   }
 
   /**
-   * Fetch a single epoch's detail for a vault (#815).
+   * Fetch a single epoch's detail for a vault (#815, #818).
    * Returns null if the vault or the epoch does not exist for it.
+   * Includes totalClaimed/totalUnclaimed for liquidity planning.
    */
   async getEpochDetail(
     contractId: string,
@@ -111,6 +112,8 @@ export class YieldService {
     yieldPerShare: string;
     netYield: string;
     distributedAt: string | null;
+    totalClaimed: string;
+    totalUnclaimed: string;
   } | null> {
     const rows = await query<{
       epoch: number;
@@ -138,6 +141,11 @@ export class YieldService {
     const row = rows[0];
     if (!row) return null;
 
+    const claimStats = await this.getEpochClaimStats(contractId, epoch);
+    const totalYield = BigInt(row.yield_amount);
+    const claimed = BigInt(claimStats.claimedAmount);
+    const unclaimed = totalYield > claimed ? totalYield - claimed : BigInt(0);
+
     return {
       epoch: row.epoch,
       yieldAmount: row.yield_amount,
@@ -145,6 +153,8 @@ export class YieldService {
       yieldPerShare: this.formatYieldPerShare(row.yield_amount, row.total_shares),
       netYield: row.net_yield ?? row.yield_amount,
       distributedAt: row.distributed_at ? row.distributed_at.toISOString() : null,
+      totalClaimed: claimed.toString(),
+      totalUnclaimed: unclaimed.toString(),
     };
   }
 
@@ -511,6 +521,195 @@ export class YieldService {
     return { data, total };
   }
 
+  // ── Epoch comparison (#820) ──────────────────────────────────────────────────
+  /**
+   * Compare two epochs side-by-side for a vault.
+   * Returns null if either epoch does not exist.
+   */
+  async compareEpochs(
+    contractId: string,
+    epochA: number,
+    epochB: number,
+  ): Promise<{
+    a: {
+      epoch: number;
+      yieldAmount: string;
+      totalShares: string;
+      yieldPerShare: string;
+      distributedAt: string | null;
+      participationRate: number;
+    };
+    b: {
+      epoch: number;
+      yieldAmount: string;
+      totalShares: string;
+      yieldPerShare: string;
+      distributedAt: string | null;
+      participationRate: number;
+    };
+    delta: {
+      yieldAmount: string;
+      yieldPerShare: string;
+    };
+  } | null> {
+    const [rowA, rowB] = await Promise.all([
+      this.getEpochDetail(contractId, epochA),
+      this.getEpochDetail(contractId, epochB),
+    ]);
+
+    if (!rowA || !rowB) return null;
+
+    const [claimA, claimB, holdersA, holdersB] = await Promise.all([
+      this.getEpochClaimStats(contractId, epochA),
+      this.getEpochClaimStats(contractId, epochB),
+      this.getEpochHolderCount(contractId, epochA),
+      this.getEpochHolderCount(contractId, epochB),
+    ]);
+
+    const participationA = this.calculateParticipationRate(claimA.uniqueClaimants, holdersA);
+    const participationB = this.calculateParticipationRate(claimB.uniqueClaimants, holdersB);
+
+    const deltaYield = BigInt(rowB.yieldAmount) - BigInt(rowA.yieldAmount);
+    const deltaYps = (() => {
+      const ypsA = this.parseYieldPerShare(rowA.yieldPerShare);
+      const ypsB = this.parseYieldPerShare(rowB.yieldPerShare);
+      return ypsB - ypsA;
+    })();
+
+    return {
+      a: {
+        epoch: rowA.epoch,
+        yieldAmount: rowA.yieldAmount,
+        totalShares: rowA.totalShares,
+        yieldPerShare: rowA.yieldPerShare,
+        distributedAt: rowA.distributedAt,
+        participationRate: participationA,
+      },
+      b: {
+        epoch: rowB.epoch,
+        yieldAmount: rowB.yieldAmount,
+        totalShares: rowB.totalShares,
+        yieldPerShare: rowB.yieldPerShare,
+        distributedAt: rowB.distributedAt,
+        participationRate: participationB,
+      },
+      delta: {
+        yieldAmount: deltaYield.toString(),
+        yieldPerShare: deltaYps.toString(),
+      },
+    };
+  }
+
+  /** Parse a "X.Y" yield-per-share string back to a BigInt of scaled units. */
+  private parseYieldPerShare(yps: string): bigint {
+    const [intPart, fracPart = ""] = yps.split(".");
+    const frac = fracPart.padEnd(18, "0").slice(0, 18);
+    return BigInt(intPart + frac);
+  }
+
+  // ── Next epoch projection (#821) ────────────────────────────────────────────
+  /**
+   * Estimate the next epoch's yield using a rolling average of the last 3 epochs.
+   * Returns null for all fields if fewer than 2 epochs exist.
+   */
+  async getNextEpochProjection(
+    contractId: string,
+  ): Promise<{
+    estimatedYieldAmount: string | null;
+    estimatedDistributionDate: string | null;
+    basedOnEpochs: number;
+  }> {
+    const rows = await query<{
+      epoch: number;
+      yield_amount: string;
+      distributed_at: Date | null;
+    }>(
+      `SELECT e.epoch, e.yield_amount, e.distributed_at
+       FROM epochs e
+       JOIN vaults v ON e.vault_id = v.id
+       WHERE v.contract_id = $1
+       ORDER BY e.epoch DESC
+       LIMIT 3`,
+      [contractId],
+    );
+
+    if (rows.length < 2) {
+      return { estimatedYieldAmount: null, estimatedDistributionDate: null, basedOnEpochs: 0 };
+    }
+
+    const epochs = rows.reverse();
+    const basedOnEpochs = epochs.length;
+
+    // Rolling average of yield amounts
+    const totalYield = epochs.reduce((sum, e) => sum + BigInt(e.yield_amount), BigInt(0));
+    const estimatedYieldAmount = (totalYield / BigInt(basedOnEpochs)).toString();
+
+    // Estimate next distribution date using average interval between epochs
+    let estimatedDistributionDate: string | null = null;
+    const distributedDates = epochs
+      .filter((e) => e.distributed_at !== null)
+      .map((e) => e.distributed_at!.getTime());
+
+    if (distributedDates.length >= 2) {
+      let totalInterval = 0;
+      for (let i = 1; i < distributedDates.length; i++) {
+        totalInterval += distributedDates[i] - distributedDates[i - 1];
+      }
+      const avgIntervalMs = totalInterval / (distributedDates.length - 1);
+      const lastDate = distributedDates[distributedDates.length - 1];
+      estimatedDistributionDate = new Date(lastDate + avgIntervalMs).toISOString();
+    }
+
+    return { estimatedYieldAmount, estimatedDistributionDate, basedOnEpochs };
+  }
+
+  // ── Epoch close webhook (#819) ─────────────────────────────────────────────
+  /**
+   * After a yield claim event, check if the epoch is now fully claimed.
+   * If so, set closed_at (idempotent) and return true so the caller can fire the webhook.
+   */
+  async closeEpochIfFullyClaimed(
+    contractId: string,
+    epoch: number,
+  ): Promise<{ closed: true; epochData: { yieldAmount: string; closedAt: string } } | null> {
+    // Check if already closed
+    const existing = await query<{ closed_at: Date | null }>(
+      `SELECT e.closed_at
+       FROM epochs e
+       JOIN vaults v ON e.vault_id = v.id
+       WHERE v.contract_id = $1 AND e.epoch = $2`,
+      [contractId, epoch],
+    );
+
+    if (existing[0]?.closed_at) return null;
+
+    const stats = await this.getEpochClaimStats(contractId, epoch);
+    const detail = await this.getEpochDetail(contractId, epoch);
+    if (!detail) return null;
+
+    if (BigInt(stats.claimedAmount) < BigInt(detail.yieldAmount)) return null;
+
+    // Set closed_at
+    await query(
+      `UPDATE epochs e
+       SET closed_at = NOW()
+       FROM vaults v
+       WHERE e.vault_id = v.id
+         AND v.contract_id = $1
+         AND e.epoch = $2
+         AND e.closed_at IS NULL`,
+      [contractId, epoch],
+    );
+
+    return {
+      closed: true,
+      epochData: {
+        yieldAmount: detail.yieldAmount,
+        closedAt: new Date().toISOString(),
+      },
+    };
+  }
+
   // ── Epoch yield distribution timeline (#822) ────────────────────────────────
   // Returns all epochs for a vault ordered by epoch number, optionally bounded
   // by ISO date filters on distributed_at. `totalInRange` is the exact sum of