About PercentGuru
PercentGuru is a free calculator site for percentage and finance maths. Every calculator shows the answer instantly, explains the formula, and walks through worked examples — so you understand the result, not just get a number.
What we cover
Two calculator hubs with 34 tools across everyday and financial maths:
- Percentage increase, decrease, and change
- Percentage difference and error
- Reverse percentage (find the original)
- Percent off, tip, and grade calculators
- GPA, fraction-to-percent, salary raise
- Annual change (CAGR) and percentage points
- Mortgage, savings, and loan payment
- Salary to hourly, simple and compound interest
- Discount, markup, and profit margin
- ROI, break-even, and cost reduction
- Sales tax, VAT, and weighted average
How we build each calculator
Every calculator page on PercentGuru follows the same standard:
- Formula sourced from authoritative references — standard mathematical definitions, accounting standards, or established textbook formulas. No approximations unless disclosed.
- Results verified with manual calculations — every formula is checked against hand-calculated examples before the page is published.
- Worked examples use real-world numbers — not abstract variables, but concrete scenarios (a £80 product, a $50,000 salary, a 3-credit university course).
- Edge cases documented — zero denominators, negative results, values over 100%, and other non-obvious situations are addressed in the FAQ of each calculator.
- Internal links connect related tools — every page links to 3–5 related calculators so you can move naturally between tools without searching.
Accuracy and limitations
All calculations run entirely in your browser using standard mathematical formulas. No data is sent to any server. No account is required.
Results are accurate to the formula definitions used. Rounding follows standard conventions (two decimal places for monetary values, up to four decimal places for percentages where relevant).
PercentGuru calculators are for informational and educational purposes. For decisions involving significant financial commitments — loans, investments, tax filings, legal obligations — verify results with a qualified accountant, financial adviser, or solicitor. The site does not provide financial or legal advice.
Who runs this site
PercentGuru is built and maintained by the PercentGuru Team — a small group focused on making everyday maths and financial calculations accessible to everyone. We built this site because we were frustrated with calculator tools that were slow, ad-heavy, or gave answers without explanation. Every page on PercentGuru is written and reviewed by us to make sure the formulas, examples, and explanations are correct and genuinely useful.
Why this site exists
Most calculator sites are built for quantity, not quality — thin pages with minimal explanation, buried under ads or slow to load. PercentGuru was built to answer the question behind the calculation, not just produce a number. When someone searches "how do I calculate percentage change", they need to understand the formula well enough to apply it themselves next time — not just get the answer to one specific instance. Every page is written with that in mind.
Contact and corrections
Found an error in a formula, a broken calculator, or a page that could be clearer? Get in touch. We read and respond to every message. Corrections are treated as priority fixes — accuracy matters more than any individual page.