TallyTools / Guides
Guides
Plain-English explanations of the maths behind the tools: the formulas, worked examples and the common mistakes to avoid.
How to calculate GST in Australia and New ZealandAdd GST, remove GST, and the divide-by-11 rule that trips people up.5 min read · goes with the GST calculatorHow many words is a 1, 5 or 10 minute speech?Word counts for speeches and talks of any length, and how to time yours.4 min read · goes with the word counterCompound interest explained, with real examplesWhy interest on interest snowballs, with worked numbers and the rule of 72.6 min read · goes with the compound interest calculatorWhat is a good typing speed?Typing speed benchmarks, what employers expect, and how to get faster.4 min read · goes with the typing speed testHow to calculate percentages: the three formulas you needPercent of, percent of a whole, and percent change, with everyday examples.5 min read · goes with the percentage calculatorHow loan repayments work, and how to pay less interestWhy early repayments are mostly interest, and three ways to pay less.6 min read · goes with the loan repayment calculatorHow to make images smaller without losing qualityPick the right format, size and quality for web, email and social.5 min read · goes with the image compressorHow to calculate your GPA, step by stepConvert grades to points, weight by credits, and work out cumulative GPA.5 min read · goes with the GPA calculator