Underdays is a London-based brand that ships to both the UK and US from dedicated fulfilment centres in each market.

We offer the following delivery methods:

Standard Delivery: $8 (free over $85)

Express Delivery: $28 (11am EST cut off)

Please note, we are unable to ship to military addresses at this stage.

We aim to fulfil your order within 1 -2 business days. During peak periods or sales, processing times may take a little longer - up to 7 business days.

Standard Delivery: 3 - 5 business days

Express Delivery: 1 - 2 business days

Please note transit times are estimates and not guaranteed.

Pre-orders: If your order includes a pre-order item, the entire order will be shipped together once the pre-order item becomes available.

**Shipping times may be affected by busy sales periods such as the holiday season.

Of course, please get in touch via team@theunderdays.com.

Please notify us of any changes as soon as possible. We’ll do our best to accommodate your request, but we can’t guarantee changes can be made once your order is in processing. If your order has already been despatched, changes cannot be made.  

Yes, we do — please visit our UK website to ship to the UK, Australia, or Europe.

No. All duties and taxes are included — there are no additional charges after placing your order.

No, only one discount code can be applied at one time.

We accept returns on eligible items under the following conditions:

• You have 30 days from the dispatch date to request a refund, exchange, or store credit.
• Items must be unworn, unwashed, and returned in their original condition, with the hygiene sticker intact and swing tag attached.
• Refunds exclude original shipping charges.
• Please allow up to 14 business days from the date your return is received for it to be processed. We’ll notify you by email once your return or exchange is complete.
• If an item does not meet our return conditions, we reserve the right to amend the return outcome accordingly.
• Items purchased during the Black Friday sale remain eligible under our standard return and exchange policy.

To initiate a return, please visit our US Returns Portal within 30 days of dispatch:

👉 theunderdays-us.loopreturns.com

All sales are final 30 days after the dispatch date.

Please note, free gifts are not returnable.

Orders that include a pre-order item(s) will be held until the pre-order item is restocked. You’ll receive an email with the estimated despatch date once your pre-order is placed.

All Underdays styles run true to size. Each product page includes a size guide— we recommend checking this before placing your order.

The Everyday range (Brief, Cheeky, Thong) is made from modal — a fabric derived from sustainably managed beechwood forests. It’s softer than cotton, naturally breathable, and retains its shape wash after wash. The Workout range uses a moisture-wicking performance fabric designed for exercise. All styles have a modal-lined gusset.

We recommend washing all our underwear on a cool wash, maximum 104°F and preferably in a garment bag.

• Air-dry flat in shade.
• Do not iron or tumble dry.
• Wash with like colours

Our core colors such as Black and Sand are always available and restocked regularly. Fashion colors and seasonal drops are limited edition — once they sell out, they won't be coming back. If you spot a color you love, we'd recommend grabbing it before it's gone. Follow us on social or sign up to our mailing list to be the first to know when new color drops land.

Bralettes are currently in development. Sign up to our mailing list at theunderdays.com to be the first to know when they launch.

We’re not perfect but we’re working on it. Click here to read more about our sustainability plans.

Our Everyday Collection is treated with HeiQ Skin Care™, Swiss synbiotic technology that supports your skin's microbiome through fabric-to-skin contact. Underwear that works like skincare. It's a cosmetic treatment that promotes skin health and appearance, not a medical product, it doesn't diagnose, treat, or prevent disease.

No, it's already built in. HeiQ Skin Care™ is embedded directly into the fabric during production, so it's working from the very first wear. No creams, sprays, or steps required.

No change to handfeel, breathability, colour, or fit, it feels exactly like the Everyday you already love. Non-irritant, human skin patch tested, and all ingredients INCI-listed.

Up to 40 washes. Wash at 30°C on a gentle cycle. Data provided by HeiQ based on testing conducted on other materials.

Not at all. UNDERskin™ is an addition to your routine, not a replacement, use it alongside your existing products.