AWS · Free tool
AWS RDS cost calculator
The line item that doubles the day Multi-AZ ships. Plug in instance, storage, replicas, and commitment to see the real monthly bill plus a side-by-side against Aurora.
Estimated monthly RDS cost
$0
$0 per year
Instance + replicas
$0
primary 730 hr × $0.171/hr
Storage + IOPS
$0
500 GB × $0.115/GB-mo
Backup beyond free
$0
7 day retention
Multi-AZ premium
$0
vs single-AZ
Side-by-side vs Aurora
If your RDS bill looks high, check these first
- Multi-AZ on dev and staging environments. Production-only is the rule, dev rarely needs failover SLA.
- gp2 storage on databases that should be on gp3. 15 to 30 percent saving with no downtime.
- No RI coverage on stable production instances. 1-year No Upfront pays for itself in four months.
- Read replicas left running after a load test, ten or twelve replicas billing primary-instance hours.
- 35-day backup retention on databases over 1 TB. Halving it shaves a four-figure line.
- Manual snapshots that nobody owns, retained forever, billing $0.095/GB-mo on databases long deleted.
Why RDS bills double overnight
The day production goes Multi-AZ, instance and storage hours double. The day you add a read replica, instance hours go up another 100 percent. The day backup retention hits 14 days on a database large enough to exceed the free tier, the snapshot line shows up. None of these changes look big in isolation. Together they explain why an RDS workload that started at $400 a month sits at $2,400 six months later.
The audit is mechanical. List every instance, flag the ones on gp2, flag the ones without RI coverage, flag the dev instances on Multi-AZ, flag the snapshots on dropped databases. We wrote up the full pattern in the quiet doubler.
Run this on your real account
Free 14-day audit, read-only IAM role, one-page CFO summary.
We pull every RDS and Aurora instance, flag missing RI coverage, gp2 holdouts, idle replicas, and orphan snapshots. The audit is free, the report is yours.
Frequently asked
Why does my RDS bill double when I enable Multi-AZ?
Multi-AZ provisions a hot standby instance in a second AZ and doubles instance hours and storage. The standby is not readable, so you also pay for read replicas if you want read scale. For dev and staging, Multi-AZ is rarely worth it. For production, the cost is the price of failover SLA.
Should I be on gp3 instead of gp2 for RDS storage?
Almost always yes. gp3 includes 12,000 IOPS and 250 MB/s for free at $0.115/GB-month. gp2 charges by volume size for IOPS at $0.10/GB-month with only 3 IOPS per GB. For most databases under 1 TB, the swap saves 15 to 30 percent on storage. The change is online with no downtime through ModifyDBInstance.
How much do Reserved Instances actually save on RDS?
A 1-year No Upfront RI saves about 30 percent on instance hours. 3-year All Upfront saves about 60 percent. Storage and backup are not eligible. RIs cover the standby on Multi-AZ and read replicas of the same class. The math is identical to EC2 RIs but the audit is easier because RDS instances are stable, long-running, and rarely shut down.
When does Aurora cost less than RDS, and when more?
Aurora Standard charges per I/O at $0.20 per million, plus $0.10/GB-month storage. For chatty workloads (over 50M I/Os per month per GB stored) Aurora I/O Optimized at $0.225/GB-month with no I/O charges is cheaper. RDS with gp3 stays cheaper than Aurora for predictable, small databases under 100 GB. Aurora Serverless v2 is its own pricing model based on ACU-seconds, useful for spiky workloads, expensive for steady ones.
How much backup storage is free?
Backup storage equal to your provisioned database storage is free. Past that, automated backups and manual snapshots cost $0.095/GB-month. Long retention windows (35 days or higher) on large databases are the most-missed line. Halve the retention or shift older snapshots to S3 lifecycle to cut the bill.
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