diff --git a/BUGS.md b/BUGS.md
index b21582d..3541dff 100644
--- a/BUGS.md
+++ b/BUGS.md
@@ -24,6 +24,20 @@ When CLOSED, move the entire entry to Resolved — don't duplicate.
   fills the cards immediately on load (and every 15 s) via REST. Needs in-car
   verification.
 
+### BUG-20 — Server trip IDs inflate far beyond the real trip count
+- **Status**: `OPEN` 2026-08-14
+- **Phase**: 29
+- **Symptom**: the portal shows trip IDs in the tens of thousands (e.g. 25136, 27091) even
+  though there are only ~10 real trips (verified: `COUNT=10`, `MAX(id)=27091`).
+- **Cause**: `trips.id` is `BIGSERIAL`, and `compute_trips_for_device()` upserts every trip on
+  every tracking batch via `INSERT … ON CONFLICT (device_id, start_time) DO UPDATE`. PostgreSQL
+  consumes a sequence value on every INSERT attempt — including the conflict/update path — so
+  the sequence advances by the trip count on every recompute (which runs after every upload
+  batch). Cosmetic only: nothing references `trips.id` as a foreign key (`deleted_trip_markers`
+  keys on `(device_id, start_time)`).
+- **Fix**: clamp the sequence to `MAX(id)` after each recompute in `compute_trips_for_device()`,
+  plus a one-time migration that renumbers existing trips compactly and resets the sequence.
+
 ---
 
 ## Resolved
diff --git a/PLAN.md b/PLAN.md
index e54e46a..4c08c26 100644
--- a/PLAN.md
+++ b/PLAN.md
@@ -2279,6 +2279,10 @@ logged as `BUG-XX` entries in [BUGS.md](./BUGS.md) (BUG-16 onward) and fixed + v
   `SET TIME!`). SIM868 CR1220 installed + its RTC set via `AT+CCLK` (was 2004 default); hold
   across power-off to confirm on next cycle. Optional follow-up: `AT+CCLK` boot-time clock
   fallback in `app_gps.py`.
+- **BUG-20 (server trip IDs inflate) — 🚧 IN PROGRESS**: `trips.id BIGSERIAL` burns sequence
+  values on every upsert (recompute runs after each upload batch), so IDs run far past the real
+  trip count (~10 trips, ids 27000+). Fix: clamp the sequence after each recompute + one-time
+  renumber migration.
 
 Open items from the drive — fill in as reported:
 - (none clock-related — BUG-17/BUG-18 closed 2026-08-14).
diff --git a/server/docker-compose.yml b/server/docker-compose.yml
index 9b7d106..5a4b152 100644
--- a/server/docker-compose.yml
+++ b/server/docker-compose.yml
@@ -14,6 +14,7 @@ services:
       - ./sql/migrate_phase25_5a.sql:/docker-entrypoint-initdb.d/migrate_phase25_5a.sql:ro
       - ./sql/migrate_phase25_5c.sql:/docker-entrypoint-initdb.d/migrate_phase25_5c.sql:ro
       - ./sql/migrate_phase26_deleted_trips.sql:/docker-entrypoint-initdb.d/migrate_phase26_deleted_trips.sql:ro
+      - ./sql/migrate_phase29_trip_ids.sql:/docker-entrypoint-initdb.d/migrate_phase29_trip_ids.sql:ro
     healthcheck:
       test: ["CMD-SHELL", "pg_isready -U ${POSTGRES_USER:-yarisobd}"]
       interval: 10s
diff --git a/server/modules/db.py b/server/modules/db.py
index 30576f7..2850b3f 100644
--- a/server/modules/db.py
+++ b/server/modules/db.py
@@ -509,6 +509,13 @@ def compute_trips_for_device(device_id):
                 """,
                 {"device_id": device_id, **t},
             )
+        # BIGSERIAL consumes a sequence value on every INSERT attempt, even when
+        # the ON CONFLICT (DO UPDATE) path is taken. Clamp the sequence back to the
+        # real max id so trip IDs don't inflate by trip_count on every recompute.
+        cur.execute(
+            "SELECT setval(pg_get_serial_sequence('trips','id'), "
+            "(SELECT COALESCE(MAX(id), 0) FROM trips))"
+        )
     return len(trips)
 
 
diff --git a/server/sql/migrate_phase29_trip_ids.sql b/server/sql/migrate_phase29_trip_ids.sql
new file mode 100644
index 0000000..e8588b9
--- /dev/null
+++ b/server/sql/migrate_phase29_trip_ids.sql
@@ -0,0 +1,26 @@
+-- Phase 29 (BUG-20): compact trip IDs and stop BIGSERIAL inflation.
+-- trips.id has no foreign-key references (deleted_trip_markers keys on
+-- (device_id, start_time)), so renumbering is purely cosmetic.
+BEGIN;
+
+-- Shift all ids up first so the compact ids (1..N) can't collide with any
+-- id that still exists during the renumber.
+UPDATE trips SET id = id + 1000000;
+
+-- Renumber compactly in start_time order.
+WITH renumbered AS (
+    SELECT id, row_number() OVER (ORDER BY start_time, id) AS new_id
+    FROM trips
+)
+UPDATE trips t
+SET id = r.new_id
+FROM renumbered r
+WHERE t.id = r.id;
+
+-- Reset the sequence to the real max id so the next insert gets MAX(id) + 1.
+SELECT setval(
+    pg_get_serial_sequence('trips', 'id'),
+    (SELECT COALESCE(MAX(id), 0) FROM trips)
+);
+
+COMMIT;