Your side hustle could be sitting in your closet. Here's how one pilates instructor made nearly $10,000 from her designer dresses.

• Charlie Hollishead is a Pilates trainer in London who rents out designer clothing as a side hustle.
• By Rotation is a peer-to-peer marketplace where people can rent designer items at a daily rate.
• Hollishead uses the money she earns on By Rotation to invest in more dresses. 

This as-told-to essay is based on an interview with Charlie Hollishead, a 28-year-old Pilates instructor who lives in London. She uses the app By Rotation to rent out dresses and accessories from her closet.

By Rotation, which launched in the US in May, is a peer-to-peer marketplace where fashion enthusiasts can rent designer items at a daily rate. For example, a three-day dress rental for a summer wedding can cost between $78 and $450, depending on the label. 

Hollishead has made £7,637 in rental sales, or about $9,812, on the By Rotation app in the past year. Insider verified her income with documentation. 

The following has been edited and condensed for clarity.

Renting my clothes is the ideal side hustle for me because I love buying dresses

I do investor relations for mining companies and teach Pilates on the side. I'm trying to move out of corporate and more into the Pilates space. 

I first heard of By Rotation earlier in the pandemic. I downloaded the app when it was still very new. I listed two items — a Prada bag and a Zimmermann dress — but didn't think too much of it. One week later, I got a notification that someone had requested to rent something. I remember being so excited. 

From there, more and more people got on the app. Now I have about 80 items listed and get requests all the time.

It's the ideal app for me because I've always loved buying dresses. But I don't know where I think I'm going to wear all of them. I don't go out that much. I'm happy that someone can put them to good use.

Now I spend the money that I make from By Rotation on buying new clothes. My monthly salary goes toward my general living expenses, and I use the money from the app to help fund my Pilates training as well. 

Here's how a rental on the By Rotation app works:

To rent an item of clothing, you upload photos of you wearing it, or you can use product photos from online. You add the brand, the size, and a description to the listing. You should let people know if there's any damage or if you've had it altered. 

Next, you input the retail value of the item, and the app suggests a rental price. For an item that's worth about £200, its suggestion will be about £10 a day. By Rotation suggests that you set the minimum rental period at three days. Once By Rotation accepts the item, people can find it through search, or they can go directly to your profile. 

When someone wants to rent your item, they send you a request with the dates and where they plan to wear it. You can either accept or decline, and when the rental goes through, By Rotation takes 15% of the total rental cost.

On the day of the rental, they can collect it from your house. I've also had people come to my office. You can also just ship it out to them. Once the rental's over, they send it back, and you get paid within about five days.

At first, I was nervous about renting my designer clothes to strangers. But I've made friends on the app. 

I remember being like, "Am I ever going to see this again?" At first, I was very scared about it. But everyone on the app is so friendly, and as soon as you have used it a few times, you feel less nervous about renting things out.

When you meet someone face-to-face, that automatically puts you at ease because you've met the person you're handing the item over to. When it comes to people renting from me, I think they feel comfortable because I've gotten a lot of good feedback.

Obviously, there are loads of people joining the app, so if a person doesn't have any reviews, that doesn't mean they're not legit. It might just be that they've just joined the platform, so it's just having a bit of a conversation with them beforehand.

I've made a few friends just by being on the app. One of the girls who rented one of my items, I'm going to dinner with her next week. It's such a nice community.

Now I see the dresses I buy as investments. They pay for themselves, and then some. 

I have a dress from Leslie Amon, and I think I bought it for maybe £300. I rent it out at £12 a day, with a two-day minimum. I've earned maybe £700 from that dress. So it not only paid for itself but also brought in an over 100% return on investment. You're not going to be making those kinds of returns on the stock market.

Now whenever I buy an item of clothing, I'm like, "Do I think this would rent?" I bought a dress a few weeks back to wear to an event. I wasn't going to it for a month, so I put it on the app. That dress has already been rented three times, and I've made half the money back on it — before even wearing it myself yet.

I have a Zimmermann dress that I can make £70 from for two days. Zimmermann does really well because the dresses are special and people love wearing them to weddings. Here in the UK, we have the (horse) races. Ascot is coming up, and people tend to want to rent Zimmermann because it has longer dresses that you wouldn't usually buy but that you might tend to rent.

I think By Rotation is mainly for special occasions, but some people do like to rent everyday wear, like I have a Charlotte Simone fluffy jacket. It's a bit of a treat to jazz up their wardrobe for that week.