diff --git a/src/lib/stores.svelte.ts b/src/lib/stores.svelte.ts
index fdc1801..96d2bfd 100644
--- a/src/lib/stores.svelte.ts
+++ b/src/lib/stores.svelte.ts
@@ -35,6 +35,9 @@ export type Task = {
   id: string;
   description: string;
   is_completed: boolean;
+  // optional
+  duration?: number;
+  stopwatchInterval?: number;
 }
 
 export type List = {
@@ -59,3 +62,18 @@ export const pinned_list = persisted<string>("pinned_list", local_lists.value![0
 export function generateId() {
   return generateRandomString(10, alphabet("a-z", "0-9"));
 }
+
+export function formatSecondsToDuration(seconds: number = 0) {
+    let hours   = Math.floor(seconds / 3600);
+    let minutes = Math.floor((seconds - (hours * 3600)) / 60);
+    seconds = seconds - (hours * 3600) - (minutes * 60);
+
+    // string ver.
+    let hrs, mins, secs;
+
+    if (hours   < 10) { hrs = "0" + hours; } else { hrs = hours; }
+    if (minutes < 10) { mins = "0" + minutes; } else { mins = minutes; }
+    if (seconds < 10) { secs = "0" + seconds; } else { secs = seconds; }
+
+    return hrs + ':' + mins + ':' + secs ;
+}
diff --git a/src/routes/[id]/+page.svelte b/src/routes/[id]/+page.svelte
index 0f9d30a..bf96091 100644
--- a/src/routes/[id]/+page.svelte
+++ b/src/routes/[id]/+page.svelte
@@ -1,8 +1,9 @@
 <script lang="ts">
   import { page } from "$app/state";
-  import { local_lists, pinned_list, generateId, type List } from "$lib/stores.svelte";
+  import { local_lists, pinned_list, generateId, type List, type Task, formatSecondsToDuration } from "$lib/stores.svelte";
   import { goto } from "$app/navigation";
   import toast from "svelte-french-toast";
+  import { onMount } from "svelte";
 
   let is_menu_open = $state(false);
   let list : List | undefined = $state(local_lists.value!.find((l) => l.id === page.params.id));
@@ -34,6 +35,24 @@
     }
   }
 
+  function toggleInterval(id: string) {
+    if (list) {
+      const task = list.tasks.find((t) => t.id === id) as Task;
+      if (task.stopwatchInterval) {
+        clearInterval(task.stopwatchInterval);
+        task.stopwatchInterval = undefined;
+      }
+      else {
+        if (!task.duration) { task.duration = 0; }
+        const interval = setInterval(() => {
+          // @ts-ignore
+          task.duration += 1;
+        }, 1000);
+        task.stopwatchInterval = interval;
+      }
+    }
+  }
+
   function createList() {
     const new_list = {
       id: generateId(),
@@ -65,6 +84,22 @@
     list = local_lists.value.find((l) => l.id === pinned_list.value);
     goto(`/${list!.id}`);
   }
+
+  onMount(() => {
+    if (list) {
+      for (const task of list.tasks) {
+        // if a task's stopwatch is still running
+        // remove it so the user can start it again in one click
+        // instead of two cause the first `toggleInterval` would
+        // just remove the interval
+        if (task.stopwatchInterval) {
+          clearInterval(task.stopwatchInterval);
+          task.stopwatchInterval = undefined;
+          local_lists.update();
+        }
+      }
+    }
+  });
 </script>
 
 <main class="flex flex-col w-full px-2 pt-8 pb-28 lg:px-4 lg:pt-4  gap-8 text-xl lg:text-3xl">
@@ -122,12 +157,14 @@
         </menu>
       {/if}
     </section>
-        <input 
-          type="text" 
-          bind:value={list.title} 
-          placeholder="Untitled"
-          class="text-5xl font-bold bg-transparent"
-        />
+
+    <input 
+      type="text" 
+      bind:value={list.title} 
+      placeholder="Untitled"
+      class="text-5xl font-bold bg-transparent"
+    />
+
     <ul class="flex flex-col gap-4">
       {#each list.tasks as task (task.id)}
         <li class="group flex justify-between items-center gap-4">
@@ -144,7 +181,13 @@
             />
           </div>
 
-          <div class="flex gap-4 w-fit">
+          <div class="flex gap-4 w-fit items-center">
+            <button
+              onclick={() => toggleInterval(task.id)} 
+              class="w-fit h-fit tabular-nums text-lg"
+            >
+              {formatSecondsToDuration(task.duration!)}
+            </button>
             <button 
               onclick={() => deleteTask(task.id)}
               class="px-4 py-2 bg-red-500 rounded-xl text-white"