diff --git a/index.js b/index.js
index f2d69dd..1056768 100644
--- a/index.js
+++ b/index.js
@@ -10,17 +10,29 @@ function sleep(n) {
     })
 }
 
+function dateToInterval(d="today") {
+    const now = DateTime.local()
+    let retDate
+    if (d == "today") {
+        retDate = now.startOf('day')
+    } else if (d == "yesterday") {
+        retDate = now.startOf('day').minus({days: 1})
+    } else {
+        retDate = DateTime.fromISO(d)
+    }
+    return Interval.fromDateTimes(retDate.startOf('day'), retDate.endOf('day'))
+}
+
 if (require.main === module) {
     (async function() {
         const m = new Marvin()
-        const d = DateTime.local()
-        const today = Interval.fromDateTimes(d.startOf('day'), d.endOf('day'))
-        const tasks = await (m.root.category('Tweag').then(tweag => tweag.tasksOverlapping(today)))
-        const value = Duration.sum(tasks.map(task => task.timeSpentOn(today))).as('hours')
+        const interval = dateToInterval(process.argv.length > 2 ? process.argv[2] : 'today')
+        const tasks = await (m.root.category('Tweag').then(tweag => tweag.tasksOverlapping(interval)))
+        const value = Duration.sum(tasks.map(task => task.timeSpentOn(interval))).as('hours')
 
         const b = new Beeminder(BEEMINDER_TOKEN)
         const goal = b.user("me").goal("loonslaven")
-        const daystamp = d.toFormat('yyyyMMdd')
+        const daystamp = interval.start.toFormat('yyyyMMdd')
         const post_data = {
             daystamp,
             value,