April 4, 2026 · Tim Fraser, Cloud Operations Lead

Why Did My AWS Bill Spike? How to Find Out in 5 Minutes

You open the AWS console on Monday morning and the bill has jumped 40%. Your manager is asking questions. You have no idea where to start.

This is one of the most common AWS panic moments — and one of the easiest to diagnose if you know where to look. Here's the fastest path from "what happened?" to "here's exactly what changed."

Step 1: Open Cost Explorer

Go to AWS Console → Billing → Cost Explorer. If it's your first time, you'll need to enable it (takes up to 24 hours to populate — do this now even if you don't need it yet).

Set the date range to the last 3 months and group by Service. This immediately tells you which service is responsible for the spike.

Common culprits:

• EC2 — instances left running (especially large ones in non-production)
• RDS — databases running 24/7 when they're only used during business hours
• S3 — data transfer costs from large downloads or cross-region replication
• NAT Gateway — these quietly add up, especially with chatty microservices
• Elastic IP — unattached IPs cost money ($3.65/mo each since the 2024 pricing change)

Step 2: Narrow the time window

Once you know the service, switch Cost Explorer to Daily granularity. Look for the exact day the cost jumped. This tells you whether it was a one-time event (someone launched something) or a gradual increase (traffic growth, log accumulation).

Step 3: Check for abandoned resources

The most common cause of bill spikes is resources that someone created and forgot about:

• EC2 → Instances: Sort by launch time. Anything launched recently that you don't recognise?
• EC2 → Volumes: Unattached EBS volumes still cost money. Filter for "available" status.
• RDS → Databases: Is there a dev-test-2 database running a db.r5.xlarge for no reason?
• Elastic Load Balancers: Each ALB costs ~$16/mo minimum, even with zero traffic.
• Elastic IPs: Go to EC2 → Elastic IPs. Any that aren't attached to a running instance?

Step 4: Check data transfer

Data transfer is the silent killer on AWS bills. Go to Cost Explorer, group by Usage Type, and filter for your suspect service. Look for:

• DataTransfer-Out-Bytes — egress to the internet
• DataTransfer-Regional-Bytes — cross-AZ traffic (often surprisingly expensive)
• S3 transfer — large files being downloaded frequently, or cross-region replication you forgot about

Step 5: Set up a budget alert (so this doesn't happen again)

Go to AWS Budgets and create a monthly cost budget. Set alerts at 80% and 100% of your expected spend. This takes 2 minutes and will save you from future surprises.

The faster way

Every step above involves clicking through the AWS console, cross-referencing services, and knowing which API calls to make. It's doable, but it takes time — especially if you're not in the console every day.

plainfra does all of this in a single question. Connect your AWS account (read-only), then ask:

> "Why did our AWS bill increase last month?"

plainfra checks Cost Explorer, scans for unused resources, analyses data transfer patterns, and gives you a prioritised breakdown with dollar amounts — in about 30 seconds.

More importantly, plainfra's weekly health reports catch these problems before they become a Monday morning crisis. A dev database left running on Friday gets flagged in Monday's report, not in next month's bill.

Even if you only use plainfra occasionally, keeping it connected means you always have an instant answer when the bill question comes up — no fumbling through consoles or waiting for Cost Explorer to load.