Probably the best Lightsail money-saver: turn $92/TB overage into $2.50/TB (free & open source)

Last year I was running a small file-distribution service on Lightsail in us-east-1. One month downloads spiked, and the bill came with $500 in data transfer overage.

The painful part: that was about 5.4 TB over the allowance, and three extra $5 IPv6-only instances (2 TB each, $15/month total) would have covered all of it.

Quick recap of how Lightsail transfer works (AWS docs + AWS Support answers on re:Post):

• Inbound and outbound both count toward the allowance, but only outbound overage is billed: $0.09/GB in US/EU regions, up to $0.17/GB in Sydney. That's ~$92/TB.
• Same region + same bundle size = one shared pool. Dual-stack and IPv6-only instances of the same size pool together.
• A $5 IPv6-only instance comes with 2 TB, so extra allowance costs ~$2.50/TB.
• Billing is hourly; an instance added mid-month gets a prorated allowance.
• Overage already incurred can't be offset later, so you need to add capacity before you run out.
• Deleting and recreating an instance does not reset this month's usage.

The trick is simple; doing the math every month isn't. So I built a calculator:

👉 https://ls.1ms.dog/

Enter the data used so far this month (or just an expected monthly total) and it tells you:

• whether you're safe, heading for overage, or already over, and how much it'll cost
• when the allowance runs out
• how many same-size traffic instances to add for the lowest total cost (compares adding 0/1/2/3, one click to apply)
• what to run next month at the current pace

Example: at the current pace this month goes 440 GB over, costing $39.58. Adding 2 traffic instances today costs $1.79, saving $37.79.

Works with AI agents. The "Use with AI" button gives you a prompt to paste into ChatGPT / Claude / Gemini / Cursor. The agent reads the site's llms.txt, runs the same rules and hands back a pre-filled link you can check. If you'd rather script it, the calculation module (calc.js) and prices (prices.json) are static files you can import cross-origin. No API key.

Free, open source, self-hostable. It's a static single page; your data stays in your browser. Host your own copy on Cloudflare Workers or Vercel (free tiers are plenty), or with Docker (amd64 + arm64):

docker run -d -p 8080:80 imxjp/lightsail-cost-saver

Source: https://github.com/yt1988/lightsail-cost-saver

Covers all 19 Lightsail regions (half-allowance regions included), 10 languages, light/dark mode, works on mobile. Estimates only; your AWS bill is final. Feedback, corrections and feature requests very welcome.