diff --git a/lib/airdrop/points.ts b/lib/airdrop/points.ts
index 1f08ae8f..881bfc06 100644
--- a/lib/airdrop/points.ts
+++ b/lib/airdrop/points.ts
@@ -5,23 +5,9 @@
  */
 
 import { AIRDROP_CONFIG } from "./config";
+import { getStreakBoost } from "./streak";
 
-/**
- * Look up the streak boost multiplier for a given streak length.
- * Returns the highest qualifying boost (e.g. streak=15 → 0.10 for the 14-day tier).
- */
-export function getStreakBoost(currentStreak: number): number {
-  const thresholds = Object.keys(AIRDROP_CONFIG.STREAK_BOOSTS)
-    .map(Number)
-    .sort((a, b) => b - a); // descending
-
-  for (const threshold of thresholds) {
-    if (currentStreak >= threshold) {
-      return AIRDROP_CONFIG.STREAK_BOOSTS[threshold];
-    }
-  }
-  return 0;
-}
+export { getStreakBoost };
 
 /**
  * Compute buy points for a trade.
diff --git a/lib/airdrop/streak.ts b/lib/airdrop/streak.ts
new file mode 100644
index 00000000..87202c84
--- /dev/null
+++ b/lib/airdrop/streak.ts
@@ -0,0 +1,56 @@
+/**
+ * Streak helpers (#882)
+ *
+ * Boost multiplier lookup, tier drop logic, and next-tier info.
+ */
+
+import { AIRDROP_CONFIG } from "./config";
+
+const TIER_THRESHOLDS = Object.keys(AIRDROP_CONFIG.STREAK_BOOSTS)
+  .map(Number)
+  .sort((a, b) => a - b); // ascending: [7, 14, 30, 50, 100]
+
+/**
+ * Look up the streak boost multiplier for a given streak length.
+ * Returns the highest qualifying boost (e.g. streak=15 → 0.10 for the 14-day tier).
+ */
+export function getStreakBoost(currentStreak: number): number {
+  for (let i = TIER_THRESHOLDS.length - 1; i >= 0; i--) {
+    if (currentStreak >= TIER_THRESHOLDS[i]) {
+      return AIRDROP_CONFIG.STREAK_BOOSTS[TIER_THRESHOLDS[i]];
+    }
+  }
+  return 0;
+}
+
+/**
+ * Drop one tier after a missed day. Returns the new streak value.
+ * Per spec: streak snaps down to the current tier's threshold.
+ *   100+ → 100, 50-99 → 50, 30-49 → 30, 14-29 → 14, 7-13 → 7, 1-6 → 0
+ */
+export function dropOneTier(streak: number): number {
+  // Find the current tier and snap to its threshold
+  for (let i = TIER_THRESHOLDS.length - 1; i >= 0; i--) {
+    if (streak >= TIER_THRESHOLDS[i]) {
+      return TIER_THRESHOLDS[i];
+    }
+  }
+  return 0;
+}
+
+/**
+ * Get the next tier info, or null if already at max.
+ */
+export function getNextTier(
+  currentStreak: number,
+): { days: number; boost: number } | null {
+  for (const threshold of TIER_THRESHOLDS) {
+    if (currentStreak < threshold) {
+      return {
+        days: threshold,
+        boost: AIRDROP_CONFIG.STREAK_BOOSTS[threshold],
+      };
+    }
+  }
+  return null; // already at max tier
+}
diff --git a/src/app/api/airdrop/checkin/route.ts b/src/app/api/airdrop/checkin/route.ts
new file mode 100644
index 00000000..1dc70d09
--- /dev/null
+++ b/src/app/api/airdrop/checkin/route.ts
@@ -0,0 +1,152 @@
+/**
+ * Streak check-in endpoint (#882)
+ *
+ * POST /api/airdrop/checkin
+ * Body: { message: string, signature: string }
+ *
+ * Verifies SIWE signature, updates streak in pl_streaks.
+ */
+
+import { NextResponse } from "next/server";
+import { verifyMessage } from "viem";
+import { createServerClient } from "../../../../../lib/supabase";
+import { AIRDROP_CONFIG } from "../../../../../lib/airdrop/config";
+import { getStreakBoost, dropOneTier, getNextTier } from "../../../../../lib/airdrop/streak";
+
+export async function POST(req: Request) {
+  const supabase = createServerClient();
+  if (!supabase) {
+    return NextResponse.json({ error: "Supabase not configured" }, { status: 500 });
+  }
+
+  let message: string;
+  let signature: `0x${string}`;
+  try {
+    const body = await req.json();
+    message = body.message;
+    signature = body.signature;
+    if (!message || !signature) throw new Error("missing fields");
+  } catch {
+    return NextResponse.json({ error: "Invalid request body" }, { status: 400 });
+  }
+
+  // Parse SIWE message to extract address
+  const addressMatch = message.match(/^(0x[a-fA-F0-9]{40})/m) ??
+    message.match(/wants you to sign in with your Ethereum account:\n(0x[a-fA-F0-9]{40})/);
+  if (!addressMatch) {
+    return NextResponse.json({ error: "Invalid SIWE message" }, { status: 400 });
+  }
+  const claimedAddress = addressMatch[1].toLowerCase();
+
+  // Verify signature
+  let valid: boolean;
+  try {
+    valid = await verifyMessage({
+      address: claimedAddress as `0x${string}`,
+      message,
+      signature,
+    });
+  } catch {
+    valid = false;
+  }
+  if (!valid) {
+    return NextResponse.json({ error: "Invalid signature" }, { status: 401 });
+  }
+
+  const now = new Date();
+
+  // Campaign window check
+  if (now < AIRDROP_CONFIG.CAMPAIGN_START || now > AIRDROP_CONFIG.CAMPAIGN_END) {
+    return NextResponse.json({ error: "Campaign not active" }, { status: 400 });
+  }
+
+  // Fetch or create streak record
+  const { data: existing } = await supabase
+    .from("pl_streaks")
+    .select("*")
+    .eq("address", claimedAddress)
+    .single();
+
+  const todayUtc = now.toISOString().slice(0, 10); // YYYY-MM-DD
+
+  if (existing?.last_checkin) {
+    const lastCheckin = new Date(existing.last_checkin);
+    const lastCheckinDay = lastCheckin.toISOString().slice(0, 10);
+
+    // Reject if same calendar day (UTC)
+    if (lastCheckinDay === todayUtc) {
+      return NextResponse.json({
+        error: "Already checked in today",
+        streak: existing.current_streak,
+        boostPercent: getStreakBoost(existing.current_streak) * 100,
+        nextTier: getNextTier(existing.current_streak),
+        checkedInToday: true,
+      }, { status: 429 });
+    }
+
+    // Reject if less than 30 minutes ago
+    const minutesSince = (now.getTime() - lastCheckin.getTime()) / (1000 * 60);
+    if (minutesSince < AIRDROP_CONFIG.STREAK_MIN_GAP_MINUTES) {
+      return NextResponse.json({
+        error: `Must wait ${AIRDROP_CONFIG.STREAK_MIN_GAP_MINUTES} minutes between check-ins`,
+      }, { status: 429 });
+    }
+  }
+
+  let newStreak: number;
+
+  if (!existing) {
+    // First ever check-in
+    newStreak = 1;
+    const { error } = await supabase.from("pl_streaks").insert({
+      address: claimedAddress,
+      current_streak: newStreak,
+      last_checkin: now.toISOString(),
+      longest_streak: newStreak,
+    });
+    if (error) {
+      console.error("[checkin] Insert failed:", error.message);
+      return NextResponse.json({ error: "Check-in failed" }, { status: 500 });
+    }
+  } else {
+    const lastCheckin = existing.last_checkin ? new Date(existing.last_checkin) : null;
+
+    if (lastCheckin) {
+      const lastDay = lastCheckin.toISOString().slice(0, 10);
+      const yesterdayUtc = new Date(now.getTime() - 86400000).toISOString().slice(0, 10);
+
+      if (lastDay === yesterdayUtc) {
+        // Consecutive day — increment streak
+        newStreak = existing.current_streak + 1;
+      } else {
+        // Missed 2+ days — snap to current tier threshold
+        newStreak = dropOneTier(existing.current_streak);
+      }
+    } else {
+      newStreak = 1;
+    }
+
+    const longestStreak = Math.max(existing.longest_streak, newStreak);
+
+    const { error } = await supabase
+      .from("pl_streaks")
+      .update({
+        current_streak: newStreak,
+        last_checkin: now.toISOString(),
+        longest_streak: longestStreak,
+      })
+      .eq("address", claimedAddress);
+
+    if (error) {
+      console.error("[checkin] Update failed:", error.message);
+      return NextResponse.json({ error: "Check-in failed" }, { status: 500 });
+    }
+  }
+
+  return NextResponse.json({
+    streak: newStreak,
+    boostPercent: getStreakBoost(newStreak) * 100,
+    nextTier: getNextTier(newStreak),
+    checkedInToday: true,
+  });
+}