Given the expense and time that goes into planning a getaway, purchasing travel insurance may seem like a no-brainer. After all, why wouldn't you protect the sizable investment you're most likely making in your summer vacation?

But before you move forward on purchasing insurance for your summer trip, make sure you're aware of the many variables involved. Squaremouth, a travel insurance comparison service, recommends avoiding these common mistakes people make when buying travel insurance.

Buying coverage too late. Travel insurance is designed to cover unforeseen events that may impact your trip—as long as you don't purchase it too late. Buying insurance early maximizes the coverage period, and gives you access to certain time-sensitive benefits for increased flexibility. Waiting too long can mean missing out on key protections like Cancel For Any Reason (CFAR), pre-existing condition coverage or coverage related to named storms during hurricane season.

Squaremouth advises buying comprehensive travel insurance coverage as soon as possible after you book your trip, ideally within 10 days of booking. This will give you access to the most possible plans and benefits.

Not being prepared for delays or disruptions. Flight delays and disruptions are on the rise, according to Squaremouth, so you may want to consider travel delay coverage that kicks in after flight delays of 3 hours, and accounts for any delay of a common carrier. This will give you the most coverage and flexibility in the event of a delay.

Paying more for "better" coverage. Many travelers assume that more expensive travel insurance offers better coverage, but that's not usually the case. Lower-cost policies aren't necessarily lower quality. Some insurance providers simply price their plans differently based on how they assess risk. Aim to buy the least expensive travel insurance policy that meets your specific coverage needs.

Buying add-on insurance from an airline or cruise line. Before opting into the insurance add-on offered by an airline or cruise line, be sure to compare other options. While these policies can provide a basic level of protection, they often come with limited coverage and less flexibility than a standalone plan. Do some comparison shopping to make sure you get what you really need.

Relying only on your credit card's coverage. Some credit cards offer travel insurance as a perk for cardholders. While these plans offer baseline coverage, like trip cancellation, trip interruption, travel delay and baggage delay coverage, there are limitations—the biggest one being a lack of medical coverage.

Make sure your investment in travel insurance provides the full spectrum of coverage—read the fine print and contact the carrier if you're not completely sure of the plan's details.