diff --git a/plan/command/add.go b/plan/command/add.go
index 3f483a9..46491b7 100644
--- a/plan/command/add.go
+++ b/plan/command/add.go
@@ -1,27 +1,35 @@
 package command
 
 import (
+	"errors"
 	"fmt"
 	"time"
 
+	"github.com/google/uuid"
 	"github.com/urfave/cli/v2"
 	"go-mod.ewintr.nl/planner/item"
 	"go-mod.ewintr.nl/planner/plan/storage"
 )
 
+var (
+	ErrInvalidArg = errors.New("invalid argument")
+)
+
 var AddCmd = &cli.Command{
 	Name:  "add",
 	Usage: "Add a new event",
 	Flags: []cli.Flag{
 		&cli.StringFlag{
-			Name:    "name",
-			Aliases: []string{"n"},
-			Usage:   "The event that will happen",
+			Name:     "name",
+			Aliases:  []string{"n"},
+			Usage:    "The event that will happen",
+			Required: true,
 		},
 		&cli.StringFlag{
-			Name:    "on",
-			Aliases: []string{"o"},
-			Usage:   "The date, in YYYY-MM-DD format",
+			Name:     "on",
+			Aliases:  []string{"o"},
+			Usage:    "The date, in YYYY-MM-DD format",
+			Required: true,
 		},
 		&cli.StringFlag{
 			Name:    "at",
@@ -37,29 +45,55 @@ var AddCmd = &cli.Command{
 }
 
 func NewAddCmd(repo storage.EventRepo) *cli.Command {
-	AddCmd.Action = NewAddAction(repo)
+	AddCmd.Action = func(cCtx *cli.Context) error {
+		return Add(cCtx.String("name"), cCtx.String("on"), cCtx.String("at"), cCtx.String("for"), repo)
+	}
 	return AddCmd
 }
 
-func NewAddAction(repo storage.EventRepo) func(*cli.Context) error {
-	return func(cCtx *cli.Context) error {
-		desc := cCtx.String("name")
-		date, err := time.Parse("2006-01-02", cCtx.String("date"))
-		if err != nil {
-			return fmt.Errorf("could not parse date: %v", err)
-		}
-
-		one := item.Event{
-			ID: "a",
-			EventBody: item.EventBody{
-				Title: desc,
-				Start: date,
-			},
-		}
-		if err := repo.Store(one); err != nil {
-			return fmt.Errorf("could not store event: %v", err)
-		}
-
-		return nil
+func Add(nameStr, onStr, atStr, frStr string, repo storage.EventRepo) error {
+	if nameStr == "" {
+		return fmt.Errorf("%w: name is required", ErrInvalidArg)
 	}
+	if onStr == "" {
+		return fmt.Errorf("%w: date is required", ErrInvalidArg)
+	}
+	if atStr == "" && frStr != "" {
+		return fmt.Errorf("%w: can not have duration without start time", ErrInvalidArg)
+	}
+	if atStr == "" && frStr == "" {
+		frStr = "24h"
+	}
+
+	startFormat := "2006-01-02"
+	startStr := onStr
+	if atStr != "" {
+		startFormat = fmt.Sprintf("%s 15:04", startFormat)
+		startStr = fmt.Sprintf("%s %s", startStr, atStr)
+	}
+	start, err := time.Parse(startFormat, startStr)
+	if err != nil {
+		return fmt.Errorf("%w: could not parse start time and date: %v", ErrInvalidArg, err)
+	}
+
+	e := item.Event{
+		ID: uuid.New().String(),
+		EventBody: item.EventBody{
+			Title: nameStr,
+			Start: start,
+		},
+	}
+
+	if frStr != "" {
+		fr, err := time.ParseDuration(frStr)
+		if err != nil {
+			return fmt.Errorf("%w: could not parse time: %s", ErrInvalidArg, err)
+		}
+		e.Duration = fr
+	}
+	if err := repo.Store(e); err != nil {
+		return fmt.Errorf("could not store event: %v", err)
+	}
+
+	return nil
 }
diff --git a/plan/command/add_test.go b/plan/command/add_test.go
new file mode 100644
index 0000000..f1b16a5
--- /dev/null
+++ b/plan/command/add_test.go
@@ -0,0 +1,131 @@
+package command_test
+
+import (
+	"testing"
+	"time"
+
+	"github.com/google/go-cmp/cmp"
+	"go-mod.ewintr.nl/planner/item"
+	"go-mod.ewintr.nl/planner/plan/command"
+	"go-mod.ewintr.nl/planner/plan/storage"
+)
+
+func TestAdd(t *testing.T) {
+	t.Parallel()
+
+	oneHour, err := time.ParseDuration("1h")
+	if err != nil {
+		t.Errorf("exp nil, got %v", err)
+	}
+	oneDay, err := time.ParseDuration("24h")
+	if err != nil {
+		t.Errorf("exp nil, got %v", err)
+	}
+
+	for _, tc := range []struct {
+		name     string
+		args     map[string]string
+		expEvent item.Event
+		expErr   bool
+	}{
+		{
+			name: "no name",
+			args: map[string]string{
+				"on":  "2024-10-01",
+				"at":  "9:00",
+				"for": "1h",
+			},
+			expErr: true,
+		},
+		{
+			name: "no date",
+			args: map[string]string{
+				"name": "event",
+				"at":   "9:00",
+				"for":  "1h",
+			},
+			expErr: true,
+		},
+		{
+			name: "duration, but no time",
+			args: map[string]string{
+				"name": "event",
+				"on":   "2024-10-01",
+				"for":  "1h",
+			},
+			expErr: true,
+		},
+		{
+			name: "time, but no duration",
+			args: map[string]string{
+				"name": "event",
+				"on":   "2024-10-01",
+				"at":   "9:00",
+			},
+			expEvent: item.Event{
+				ID: "a",
+				EventBody: item.EventBody{
+					Title: "event",
+					Start: time.Date(2024, 10, 1, 9, 0, 0, 0, time.UTC),
+				},
+			},
+		},
+		{
+			name: "no time, no duration",
+			args: map[string]string{
+				"name": "event",
+				"on":   "2024-10-01",
+			},
+			expEvent: item.Event{
+				ID: "a",
+				EventBody: item.EventBody{
+					Title:    "event",
+					Start:    time.Date(2024, 10, 1, 0, 0, 0, 0, time.UTC),
+					Duration: oneDay,
+				},
+			},
+		},
+		{
+			name: "full",
+			args: map[string]string{
+				"name": "event",
+				"on":   "2024-10-01",
+				"at":   "9:00",
+				"for":  "1h",
+			},
+			expEvent: item.Event{
+				ID: "a",
+				EventBody: item.EventBody{
+					Title:    "event",
+					Start:    time.Date(2024, 10, 1, 9, 0, 0, 0, time.UTC),
+					Duration: oneHour,
+				},
+			},
+		},
+	} {
+		t.Run(tc.name, func(t *testing.T) {
+			mem := storage.NewMemory()
+			actErr := command.Add(tc.args["name"], tc.args["on"], tc.args["at"], tc.args["for"], mem) != nil
+			if tc.expErr != actErr {
+				t.Errorf("exp %v, got %v", tc.expErr, actErr)
+			}
+			if tc.expErr {
+				return
+			}
+			actEvents, err := mem.FindAll()
+			if err != nil {
+				t.Errorf("exp nil, got %v", err)
+			}
+			if len(actEvents) != 1 {
+				t.Errorf("exp 1, got %d", len(actEvents))
+			}
+			if actEvents[0].ID == "" {
+				t.Errorf("exp string not te be empty")
+			}
+			tc.expEvent.ID = actEvents[0].ID
+			if diff := cmp.Diff(tc.expEvent, actEvents[0]); diff != "" {
+				t.Errorf("(exp +, got -)\n%s", diff)
+			}
+		})
+	}
+}