About NumberSwift

NumberSwift is a collection of free calculators for technology, personal finance and mathematics, operated by Alejandro del Alamo. Each tool combines an interactive calculation with its formula, a worked example and the assumptions needed to interpret the answer.

Practical tools with visible reasoning

A download estimate should explain bits and bytes. A loan payment should distinguish principal and interest from extra costs. A percentage comparison should identify its baseline. We put these details alongside the result so you can check whether the model fits your question.

How calculations are checked

We use internal formula reviews and automated checks against known examples and boundary cases. References explain the underlying definitions and methods; they do not imply endorsement or professional certification. See our calculation and editorial methodology.

Privacy and access

You can use the calculators without an account. Calculations run in your browser. Shared calculation links can contain the values you choose to share, so avoid including sensitive information. Read the privacy policy for site-level data handling.

Corrections and contact

If a result looks wrong, send a reproducible example with the tool name, input units and expected answer. Do not send account numbers or private financial documents.

Explore the technology calculators, finance calculators and math calculators.