If you will be in Copenhagen for an extended period of time, such as a semester abroad, then getting a bike is a great way to immerse yourself in the Danish culture. It is very easy to get ripped off or go to the wrong places if you do not know what to look for. Although renting and buying new bikes is a viable option, buying secondhand is probably your best bet. You should look for a bike that’s in the 500-1500 dkk range.
Bikes are typically sold for the cheapest prices in Facebook groups, such as CIP Second Hand Bike Copenhagen or ESN CPH: Give-Buy-Sell-Rent. There are daily posts describing bikes for sale, often accompanied with a picture and an asking price. All you have to do is message the seller expressing your interest, and then meet the seller in person to try out the bike and exchange money.
Although bikes in Facebook groups are often in good quality, you may feel safer knowing your bike is coming from a bike shop. There are plenty of decently priced bike shops on the street Nørrebrogade. Local universities often recommend Copenhagen Bicycles because they guarantee buy-back when you permanently leave the city, but the bikes are relatively expensive compared to the suggestions listed above. Copenhagen is filled with bike shops, so you can always just explore your neighborhood and see what you find.
A bike with a basket is highly favorable. Once you have a bike, it will become your main mode of transportation, so a little extra storage space cannot hurt. If you don’t know where you are heading, you can leave your phone in your basket and use GPS to bring you to your next destination. Additionally, a basket is super convenient for grocery shopping.
Copenhagen is relatively flat, so it does not really matter how many gears your bike has. As long as your bike has working breaks, you are good to go. Be sure to buy lights for your bike, not only so people and cars can see you, but also because it is required by law for lights to be on from sunset to sunrise while riding.
Lastly, buy a bike lock! Copenhagen is a safe city, but the biggest crime here is bike theft. Do not be the person to get their bike stolen within the first week of your purchase.