I will give you an E-commerce Profit Calculator

(READ THE FULL GUIDE FIRST BEFORE ANYTHING)
What this product is
A single web page that runs in your browser and tracks:

Products: The exact profit and margin of every item you sell.

Sales: Log a sale and it auto-calculates the revenue and profit.

Expenses: Track overhead costs like ads and packaging.

Dashboard: See your total revenue, true net profit, and top-performing products at a glance.

It looks like software. It installs like a file. It stores your data only in your browser — never on a server.
What this product is not
It is not an inventory management system (it doesn't track stock levels).

It is not synced across devices (each browser keeps its own copy — see "Backup" on page 8).

It is not a subscription (you bought it once, you own it forever)
Why this is good
No account to create

No subscription to renew

No company can read your sales or profit data

Works offline

Free forever

Why this is a trade-off
If you clear your browser data (Settings → Clear browsing data), your records disappear.

If you open the file in a different browser, you get a different, empty copy.

If you move the file to another computer, the file moves but the data doesn't
How to protect yourself
Export a backup every week (or after every significant entry): Settings → Export backup (.json). It downloads a small file like profit-calculator-backup.json.

Store it wherever you back up other important files: Google Drive, Dropbox, an external drive, or email it to yourself.

To restore a backup: Settings → Restore from backup → pick the .json file. Everything comes back.

One habit that saves people hours
Export a backup before clicking "Reset to sample data" or before a big re-organization. Exporting is one click. Re-entering a year of sales is not.