Plain-language terms for buying and using Otter Numbers calculators. Last updated July 2026.
What you're buying
Each product is a downloadable spreadsheet file (Excel .xlsx) that opens in Excel, Google Sheets, or Numbers. When you buy one, you get a personal licence to use it for your own personal or business purposes. Please don't resell, redistribute, or republish the files.
Estimates only
Every calculator is a planning estimator, not professional advice or an official filing tool. We build and check each one carefully and cite our sources, but figures depend on inputs and assumptions that can vary. Always confirm the numbers yourself before relying on them for an important decision. See Why Trust These Numbers for exactly how each one is verified.
Payments
Payments are processed securely by Stripe. Your card details are entered on Stripe's own checkout page — they are never seen by or stored on this website. Prices are shown in the currency listed on each product and charged as a single one-time payment. There are no subscriptions.
Otter Numbers is operated by Rumble Design Store, which processes payments through Stripe. Your card statement and receipt may show a name associated with that account.
Refunds
We want you to be happy with what you buy. Because these are instant digital downloads:
- If a calculator has an error, or doesn't do what its product page describes, you'll get a full refund — just email us within 30 days.
- For a simple change of mind after downloading, we generally can't offer a refund, since the file has already been delivered. If something's genuinely wrong, get in touch and we'll make it right.
Support
Questions, problems, refund requests, or something that looks off in a calculator? Email rumblechow@gmail.com and we'll get back to you, usually within a couple of business days.
Changes
We may update these terms from time to time; the "last updated" date above will change when we do. When a calculator's underlying rates or standards change, we publish a new dated version rather than silently altering the one you bought.