diff --git a/internal/json_store.go b/internal/json_store.go
index ad43c91..f0268ce 100644
--- a/internal/json_store.go
+++ b/internal/json_store.go
@@ -96,11 +96,9 @@ func (fs *JSONStore) Load(ctx context.Context) (map[string]*FillerQueue, error)
 // the same directory followed by an atomic rename so a crash mid-write cannot
 // leave a half-written state file.
 func (fs *JSONStore) Save(ctx context.Context, queue map[string]*FillerQueue) error {
-	state := State{
-		Version:  StateVersion,
-		Platform: fs.platform,
-		Queues:   make(map[string][]persistedFiller),
-	}
+	queues := make(map[string][]persistedFiller)
+	latest := time.Time{}
+	earliest := time.Time{}
 
 	for symbol, q := range queue {
 		if q == nil || q.Len() == 0 {
@@ -119,8 +117,23 @@ func (fs *JSONStore) Save(ctx context.Context, queue map[string]*FillerQueue) er
 				Price:      f.Price(),
 				Filled:     f.Filled(),
 			})
+
+			if f.Timestamp().After(latest) {
+				latest = f.Timestamp()
+			}
+			if f.Timestamp().Before(earliest) || earliest.IsZero() {
+				earliest = f.Timestamp()
+			}
 		}
-		state.Queues[symbol] = persisted
+		queues[symbol] = persisted
+	}
+
+	state := State{
+		Version:  StateVersion,
+		Platform: fs.platform,
+		Queues:   queues,
+		Latest:   latest,
+		Earliest: earliest,
 	}
 
 	buf := &bytes.Buffer{}
diff --git a/internal/json_store_test.go b/internal/json_store_test.go
index 6ec0539..93856fe 100644
--- a/internal/json_store_test.go
+++ b/internal/json_store_test.go
@@ -9,6 +9,7 @@ import (
 	"path/filepath"
 	"strings"
 	"testing"
+	"time"
 
 	"github.com/nmoniz/any2anexoj/internal"
 	"github.com/nmoniz/any2anexoj/internal/mocks"
@@ -84,13 +85,25 @@ func TestJSONStore_RoundTrip(t *testing.T) {
 	// confirming the inline form is parseable guards against accidentally
 	// double-encoding it again in the future).
 	var parsed struct {
-		Queues map[string][]struct {
+		Latest   time.Time `json:"latest"`
+		Earliest time.Time `json:"earliest"`
+		Queues   map[string][]struct {
 			RecordData json.RawMessage `json:"record_data"`
 		} `json:"queues"`
 	}
 	if err := json.Unmarshal(data, &parsed); err != nil {
 		t.Fatalf("saved state file is not valid JSON: %v", err)
 	}
+
+	// The latest/earliest bounds must be persisted alongside the queues.
+	// Every record in this test returns testRecordTime, so both bounds must
+	// equal it exactly.
+	if !parsed.Latest.Equal(testRecordTime) {
+		t.Errorf("state latest = %v; want %v", parsed.Latest, testRecordTime)
+	}
+	if !parsed.Earliest.Equal(testRecordTime) {
+		t.Errorf("state earliest = %v; want %v", parsed.Earliest, testRecordTime)
+	}
 	for symbol, lots := range parsed.Queues {
 		for i, lot := range lots {
 			if len(lot.RecordData) == 0 {
@@ -341,13 +354,20 @@ func TestNewJSONStore_ValidatesArguments(t *testing.T) {
 	}
 }
 
-// newRecord builds a MockRecord whose Symbol() returns the given symbol.
-// The JSONStore only reads Symbol() off the loaded Record during tests
-// (quantity/price/filled come from the persisted struct fields), so all
-// other Record methods can be left as default-mocked values.
+// testRecordTime is the deterministic timestamp returned by every record
+// built in this file. Using a fixed value keeps the latest/earliest bounds
+// written by JSONStore.Save predictable and assertable.
+var testRecordTime = time.Date(2024, 6, 15, 12, 0, 0, 0, time.UTC)
+
+// newRecord builds a MockRecord whose Symbol() returns the given symbol and
+// whose Timestamp() returns testRecordTime. The JSONStore only reads Symbol()
+// and Timestamp() off the Record during tests (quantity/price/filled come
+// from the persisted struct fields), so all other Record methods can be left
+// as default-mocked values.
 func newRecord(ctrl *gomock.Controller, symbol string) *mocks.MockRecord {
 	r := mocks.NewMockRecord(ctrl)
 	r.EXPECT().Symbol().Return(symbol).AnyTimes()
+	r.EXPECT().Timestamp().Return(testRecordTime).AnyTimes()
 	return r
 }
 
diff --git a/internal/state.go b/internal/state.go
index 10cb8c2..53ae36b 100644
--- a/internal/state.go
+++ b/internal/state.go
@@ -3,6 +3,7 @@ package internal
 import (
 	"context"
 	"encoding/json"
+	"time"
 
 	"github.com/shopspring/decimal"
 )
@@ -15,6 +16,8 @@ const StateVersion = "2"
 type State struct {
 	Version  string                       `json:"version"`
 	Platform string                       `json:"platform"`
+	Latest   time.Time                    `json:"latest"`
+	Earliest time.Time                    `json:"earliest"`
 	Queues   map[string][]persistedFiller `json:"queues"`
 }