How Does the Lightsail 90-Day Free Trial Work with Multiple Instances?

The Amazon Lightsail 90-day free trial works based on hours of usage rather than days, and it's calculated separately for each instance type (Linux/Unix and Windows). Here's how it works:

1. You get 750 free hours per month for 3 months (90 days) for eligible Lightsail plans.

2. These 750 hours can be used across multiple instances of the same type. For example, if you're running 3 Linux instances, their usage hours are combined and counted against the 750-hour monthly limit.

3. Running multiple instances simultaneously will consume the free hours faster. For instance, running 3 instances for 24 hours would use 72 hours of your free allocation (3 x 24 = 72).

4. The trial doesn't end early if you use all 750 hours before the month is over. Instead, you'll start incurring charges for usage beyond 750 hours in that month.

5. The free trial applies separately to Linux/Unix and Windows instances. This means you could potentially run both a Linux and a Windows instance continuously for the entire 90-day period without extra charges, as long as you stay within the eligible plans.

6. The trial period lasts for a full 90 days from when you launch your first eligible resource, regardless of how quickly you use the free hours.

To avoid unexpected charges, it's important to monitor your usage, especially when running multiple instances. Remember that if you exceed the 750 hours per month or choose a plan not included in the free trial, you will be charged for the excess usage or non-eligible plan.
Sources
Lightsail free tier specifications (3 months / 90 days) | AWS re:Post
Lightsail 3 Months Trial - Windows and Linux seperate? | AWS re:Post
Billing and account management - Amazon Lightsail
How Free hours calculation works? | AWS re:Post