TL;DR – What You Need to Know
- Where to redeem: englishtest.duolingo.com only – not duolingo.com or the language-learning app
- What you need: your voucher code (from your Comet confirmation email), a free DET account, and a payment method on file (even though the balance will be $0)
- Where the code goes: the “Voucher code” or “Promo code” field at checkout, applied before you confirm your booking
- Most common error: extra spaces or line breaks copied along with the code – always copy-paste, never retype
- Codes are single-use. Once applied successfully, it can’t be redeemed again
Table of Contents
- Before you start: what you’ll need
- Step-by-step: redeeming your voucher code
- What the checkout screen should look like at each stage
- Redeeming on mobile vs desktop
- Troubleshooting every common error
- What happens immediately after redemption
- Rescheduling, cancelling, and the 21-day window
- Redeeming a voucher bought for someone else
- Common mistakes that aren’t actually errors
- Frequently asked questions
- Next steps
Before you start: what you’ll need
Redemption takes under two minutes if you have everything ready. Before you begin, make sure you have:
- Your voucher code, from the confirmation email sent after your Comet purchase. Keep this email open in a separate tab, since you’ll copy-paste the code directly from it.
- A DET account. If you don’t already have one, you’ll create it for free during Step 1 below, using the same email address you plan to use for your applications.
- A payment method on file, even though your final balance will be $0 once the code is applied. Duolingo’s checkout flow requires a card on file as standard practice, though nothing will be charged if the voucher covers the full amount.
- A stable internet connection and a standard browser (Chrome, Safari, or Firefox). Avoid redeeming through an in-app browser (for example, tapping the link directly from within an email or messaging app), which can sometimes interfere with the voucher field.
Step-by-step: redeeming your voucher code
Step 1: Go to englishtest.duolingo.com and log in or create an account.
This is the dedicated DET test-taking platform, a completely separate site from duolingo.com (the language-learning app). Confirming you’re on the right URL before doing anything else avoids the single most common point of confusion. If you don’t have an account yet, sign up using the same name and email you’ll use on your university applications, since your certified score report will be tied to this account.
Step 2: Click “Buy a test” to reach the checkout page.
This takes you to Duolingo’s official payment screen, where the price is shown as $70 USD by default before any code is applied.
Step 3: Find the “Voucher code” or “Promo code” field.
It’s typically located just below the price summary, above the final payment button. It may be collapsed under a small “Have a code?” link, so look for that if the field isn’t immediately visible.
Step 4: Copy your code directly from your Comet confirmation email and paste it into the field.
Don’t retype it manually. Voucher codes are case-sensitive and often include a mix of numbers, letters, and symbols where a small typing error (mistaking a zero for the letter O, for instance) will cause it to fail. Copy-pasting eliminates this entirely.
Step 5: Click “Apply.”
If the code is valid and unused, the displayed price should update immediately from $70 to $0.
Step 6: Complete the booking.
Confirm your details and finish checkout. Since the balance is $0, no payment is actually processed, but you’ll still need to click through the confirmation to finalise your booking.
Step 7: Choose when to take the test.
Once booked, you can start the test immediately (DET is available 24/7) or save it for later within your 21-day window. There’s no fixed appointment to schedule.
What the checkout screen should look like at each stage
Since screenshots vary slightly as Duolingo updates its interface, here’s what to expect functionally at each stage, so you know you’re on track:
- Before entering a code: price shows $70 USD, a “Pay” or “Continue” button is visible, and a smaller “Voucher code” or “Have a promo code?” link or field sits near the price
- After entering a valid, unused code and clicking Apply: the price updates to $0.00, sometimes with a small confirmation message like “Voucher applied” or a strikethrough on the original $70 price
- After clicking Apply with an invalid or already-used code: an error message appears near the field, usually saying something like “Invalid code” or “This code has already been used,” and the price remains at $70
- After successful checkout: you’re taken to your account dashboard, where your test appears as “Ready to take” with a 21-day countdown
If your screen doesn’t match one of these patterns after following the steps exactly, move to the troubleshooting section below before contacting support.
Redeeming on mobile vs desktop
Redemption works on both, but desktop is the more reliable option, mainly because copy-pasting a long code between a separate email app and a mobile browser introduces more opportunities for an accidental extra space or line break.
If you’re redeeming on mobile:
- Open your Comet confirmation email in your phone’s email app, not through a notification preview, which sometimes truncates the code
- Long-press to select and copy the full code carefully, checking that you haven’t included a trailing space
- Open englishtest.duolingo.com in your phone’s standard browser (Safari or Chrome), not an in-app browser
- Paste directly into the voucher field rather than switching between apps multiple times, which increases the chance of copying stale clipboard content by mistake
If anything goes wrong on mobile, switching to a desktop browser and repeating the same copy-paste process resolves the large majority of redemption issues.
Troubleshooting every common error
“Invalid code” immediately after pasting.
This is almost always an extra space or line break copied along with the code. Re-copy the code directly from your confirmation email, and paste it into a plain text field (like your browser’s address bar) first to check for hidden characters, then copy it again from there into the voucher field.
“This code has already been used.”
Voucher codes are single-use. If you’re seeing this on what you believe is your first attempt, double-check you copied the correct code, especially if you have more than one Comet confirmation email in your inbox from previous purchases or comparisons. If you’re confident the code hasn’t been used and you’re still seeing this error, contact Comet support with your order confirmation.
The voucher field doesn’t appear at all.
Make sure you’re on englishtest.duolingo.com, not duolingo.com. The regular language-learning app has no relationship to DET vouchers and won’t have this field anywhere in its interface.
The price doesn’t update after clicking “Apply.”
Try refreshing the checkout page and re-pasting the code once more. If it still doesn’t update, an ad blocker or VPN extension may be interfering with the checkout script; try a private/incognito browser window with extensions disabled.
Payment fails even though the balance shows $0.
Some checkout flows still validate that a payment method is on file, even when nothing will be charged. Add any valid card to proceed; it will not be billed if the voucher fully covers the cost.
Code works but the test type or bundle option looks wrong.
Confirm you purchased the correct voucher type (a single test) rather than accidentally comparing it against the bundle option on the checkout page, since these have separate flows.
Still not working after trying all of the above?
Contact Comet’s support team directly with your order confirmation number and a screenshot of the exact error message. This is faster than contacting Duolingo support directly, since Comet can verify your voucher’s status immediately.
What happens immediately after redemption
Once your code is successfully applied and your booking is confirmed:
Your test is ready to take within a 21-day window. You can start immediately or schedule it for whenever suits you within that period; there’s no fixed appointment slot to book.
You’ll need about one uninterrupted hour, a quiet, private room, a computer with a working camera and microphone, a stable internet connection, and a secondary device (phone or tablet) propped to show your desk as a second camera angle.
Results typically arrive within 24-48 hours after you complete the test, sent to the email associated with your DET account.
You can then send your score to unlimited universities for free, directly from your DET account dashboard, with no extra charge no matter how many institutions you send to.
Rescheduling, cancelling, and the 21-day window
Your voucher-redeemed test booking follows the same rules as any standard DET purchase:
- You have 21 days from redemption to take the test. If you don’t complete it within this window, the booking is cancelled and cannot be recovered, so don’t redeem your voucher significantly earlier than you actually plan to test.
- The booking isn’t tied to a specific date or time. You can take the test any hour of any day within your 21-day window.
- Cancelling or failing to test within the window forfeits the booking entirely, with no refund or option to reapply the same voucher, since it’s already been marked as used at the point of redemption.
Because of this, the best sequence is: prepare first, then buy and redeem your voucher only once you’re genuinely ready to test within the next few weeks. See our DET preparation guide if you haven’t started studying yet.
Redeeming a voucher bought for someone else
If you purchased a Comet voucher on behalf of another student (a common scenario for parents, counsellors, or agents), the redemption process is identical, but a few details matter:
- The DET account used at redemption must belong to the actual test-taker, since the score report and video interview are tied to that individual’s identity verification.
- Forward the confirmation email directly to the test-taker, or share the voucher code securely, rather than redeeming it yourself on their behalf using their login, which can complicate identity verification during the test.
- The test-taker will need their own government-issued ID for verification when they sit the test, regardless of who purchased the voucher.
Common mistakes that aren’t actually errors
Seeing the $70 price briefly before the code is applied. This is normal; the field only updates the price after you click “Apply,” not automatically as you type.
Being asked for a payment method despite a $0 balance. Standard checkout behaviour, not a sign anything is wrong. No charge will be processed.
Not receiving an immediate confirmation email after redemption. Check your spam folder first; if it’s genuinely missing after a few minutes, your account dashboard will still show the test as booked even without the email arriving.
The test not appearing available “right now.” As long as the booking shows within your 21-day window on your dashboard, you can start whenever you’re ready; there’s no separate activation step required.
Frequently asked questions
Only at englishtest.duolingo.com, the dedicated test-taking platform. This is a different site from duolingo.com, the language-learning app, which has no voucher redemption function.
The most common cause is an extra space or line break copied along with the code. Copy it directly from your confirmation email and paste it without retyping. If the issue persists, confirm you’re on englishtest.duolingo.com and try a private browser window with extensions disabled.
No. Each code is single-use. Once successfully applied and a booking is confirmed, it cannot be reused.
Often yes, as standard checkout practice, even though your final balance will be $0 and nothing will be charged.
21 days from the point of redemption. If you don’t complete the test within this window, the booking is cancelled and cannot be recovered.
The purchase can be made by anyone, but redemption should happen under the actual test-taker’s own DET account, since the score report and identity verification are tied to that individual.
Check your Comet confirmation email first, including your spam folder. If you genuinely can’t locate it, contact Comet support with your order details to have it resent.
Yes, functionally, though desktop is generally more reliable for copy-pasting the code cleanly. If you run into trouble on mobile, switching to a desktop browser resolves most issues.
Double-check you copied the correct code, particularly if you have multiple confirmation emails in your inbox. If you’re confident it hasn’t been used, contact Comet support with your order confirmation for verification.
No. The voucher fully covers the $70 test fee (since you already paid $60 to Comet), and redemption itself carries no additional charge.
Next steps
Haven’t bought your voucher yet? Get one from Comet for $60, delivered to your inbox in under a minute. Already redeemed and ready to prepare? Our DET study plan covers exactly what to focus on before test day.
→ Get your DET voucher for $60 – instant delivery
Related guides from Cialfo:
- How to Get a DET Voucher at a Discount in 2026
- DET vs IELTS vs TOEFL vs PTE: Which Test Should You Take?
- DET Scores Explained: What’s a Good Score?
- How Much Does the Duolingo English Test Really Cost?
- How to Prepare for the Duolingo English Test
- Universities That Accept the Duolingo English Test
- The Complete Guide to the Duolingo English Test
