Pro Calculators and Guides

Specialist calculators are only useful when you understand the rules behind the numbers. These guides explain what each professional calculator does, which inputs matter, how to read the result and where the official rules come from, covering payroll and tax, immigration and visas, housing, business compliance, engineering and science. Every guide links to a free tool that runs in your browser and keeps your figures private.

318 guides

How to Encode and Decode HTML Entities (& < > and More)

Turn special characters into HTML entities so text shows correctly in a web page, or decode entities back to normal text.

15 Oct 2026

Pro Calculators and Guides

How to Encode and Decode URLs (Percent Encoding Explained)

Make text safe to put in a web address, or turn %20-style codes back into normal words. Includes the difference between encoding a whole link and a part.

15 Oct 2026

Pro Calculators and Guides

How to Estimate Bricks and Concrete for a Wall or Slab

Work out the number of bricks for a wall or the cement, sand and aggregate for a concrete slab, with a waste allowance.

15 Oct 2026

Pro Calculators and Guides

How to Estimate Ovulation and Your Fertile Window From Your Cycle

Use the first day of your last period and your usual cycle length to estimate the next period, ovulation day and fertile window, and know the limits.

15 Oct 2026

Pro Calculators and Guides

How to Estimate Reading Time and Speaking Time for Any Text

Paste an article, speech or essay and see how long it takes to read silently or say out loud, with an adjustable speed.

15 Oct 2026

Pro Calculators and Guides

How to Estimate Stamp Duty (SDLT) When Buying a Home in England or Northern Ireland

Understand how Stamp Duty Land Tax is charged in bands, how first-time buyer relief and the additional property surcharge work, and estimate your bill.

15 Oct 2026