diff --git a/plan/storage/memory.go b/plan/storage/memory.go
index 2100eb7..ce08fb7 100644
--- a/plan/storage/memory.go
+++ b/plan/storage/memory.go
@@ -9,13 +9,15 @@ import (
 )
 
 type Memory struct {
-	events map[string]item.Event
-	mutex  sync.RWMutex
+	events   map[string]item.Event
+	localIDs map[int]string
+	mutex    sync.RWMutex
 }
 
 func NewMemory() *Memory {
 	return &Memory{
-		events: make(map[string]item.Event),
+		events:   make(map[string]item.Event),
+		localIDs: make(map[int]string),
 	}
 }
 
@@ -30,7 +32,23 @@ func (r *Memory) Find(id string) (item.Event, error) {
 	return event, nil
 }
 
-func (r *Memory) FindAll() ([]item.Event, error) {
+func (r *Memory) FindByLocal(localID int) (item.Event, error) {
+	r.mutex.RLock()
+	defer r.mutex.RUnlock()
+
+	id, exists := r.localIDs[localID]
+	if !exists {
+		return item.Event{}, errors.New("event not found")
+	}
+
+	event, exists := r.events[id]
+	if !exists {
+		return item.Event{}, errors.New("id an localid mismatch")
+	}
+	return event, nil
+}
+
+func (r *Memory) FindAll() (map[int]string, []item.Event, error) {
 	r.mutex.RLock()
 	defer r.mutex.RUnlock()
 
@@ -42,14 +60,24 @@ func (r *Memory) FindAll() ([]item.Event, error) {
 		return events[i].ID < events[j].ID
 	})
 
-	return events, nil
+	return r.localIDs, events, nil
 }
 
 func (r *Memory) Store(e item.Event) error {
 	r.mutex.Lock()
 	defer r.mutex.Unlock()
 
+	if _, exists := r.events[e.ID]; !exists {
+		cur := make([]int, 0, len(r.localIDs))
+		for i := range r.localIDs {
+			cur = append(cur, i)
+		}
+		localID := NextLocalID(cur)
+		r.localIDs[localID] = e.ID
+	}
+
 	r.events[e.ID] = e
+
 	return nil
 }
 
@@ -61,5 +89,12 @@ func (r *Memory) Delete(id string) error {
 		return errors.New("event not found")
 	}
 	delete(r.events, id)
+
+	for localID, eventID := range r.localIDs {
+		if id == eventID {
+			delete(r.localIDs, localID)
+		}
+	}
+
 	return nil
 }
diff --git a/plan/storage/storage.go b/plan/storage/storage.go
index 3e8369d..335e220 100644
--- a/plan/storage/storage.go
+++ b/plan/storage/storage.go
@@ -1,6 +1,10 @@
 package storage
 
-import "go-mod.ewintr.nl/planner/item"
+import (
+	"sort"
+
+	"go-mod.ewintr.nl/planner/item"
+)
 
 type EventRepo interface {
 	Store(event item.Event) error
@@ -8,3 +12,39 @@ type EventRepo interface {
 	FindAll() ([]item.Event, error)
 	Delete(id string) error
 }
+
+func NextLocalID(used []int) int {
+	if len(used) == 0 {
+		return 1
+	}
+
+	sort.Ints(used)
+	usedMax := 1
+	for _, u := range used {
+		if u > usedMax {
+			usedMax = u
+		}
+	}
+
+	var limit int
+	for limit = 1; limit <= len(used) || limit < usedMax; limit *= 10 {
+	}
+
+	newId := used[len(used)-1] + 1
+	if newId < limit {
+		return newId
+	}
+
+	usedMap := map[int]bool{}
+	for _, u := range used {
+		usedMap[u] = true
+	}
+
+	for i := 1; i < limit; i++ {
+		if _, ok := usedMap[i]; !ok {
+			return i
+		}
+	}
+
+	return limit
+}
diff --git a/plan/storage/storage_test.go b/plan/storage/storage_test.go
new file mode 100644
index 0000000..528ec1a
--- /dev/null
+++ b/plan/storage/storage_test.go
@@ -0,0 +1,76 @@
+package storage_test
+
+import (
+	"testing"
+
+	"go-mod.ewintr.nl/planner/plan/storage"
+)
+
+func TestNextLocalId(t *testing.T) {
+	for _, tc := range []struct {
+		name string
+		used []int
+		exp  int
+	}{
+		{
+			name: "empty",
+			used: []int{},
+			exp:  1,
+		},
+		{
+			name: "not empty",
+			used: []int{5},
+			exp:  6,
+		},
+		{
+			name: "multiple",
+			used: []int{2, 3, 4},
+			exp:  5,
+		},
+		{
+			name: "holes",
+			used: []int{1, 5, 8},
+			exp:  9,
+		},
+		{
+			name: "expand limit",
+			used: []int{1, 2, 3, 4, 5, 6, 7, 8, 9, 10},
+			exp:  11,
+		},
+		{
+			name: "wrap if possible",
+			used: []int{8, 9},
+			exp:  1,
+		},
+		{
+			name: "find hole",
+			used: []int{1, 2, 3, 4, 5, 7, 8, 9},
+			exp:  6,
+		},
+		{
+			name: "dont wrap if expanded before",
+			used: []int{15, 16},
+			exp:  17,
+		},
+		{
+			name: "do wrap if expanded limit is reached",
+			used: []int{99},
+			exp:  1,
+		},
+		{
+			name: "sync bug",
+			used: []int{151, 956, 955, 150, 154, 155, 145, 144,
+				136, 152, 148, 146, 934, 149, 937, 135, 140, 139,
+				143, 137, 153, 939, 138, 953, 147, 141, 938, 142,
+			},
+			exp: 957,
+		},
+	} {
+		t.Run(tc.name, func(t *testing.T) {
+			act := storage.NextLocalID(tc.used)
+			if tc.exp != act {
+				t.Errorf("exp %v, got %v", tc.exp, act)
+			}
+		})
+	}
+}