How the numbers work

The guides on this site show their arithmetic rather than asserting a result. There are 1,643 worked calculations across 232 guides, made up of 6,520 individual lines, and this gathers them by subject.

A calculator gives you an answer. These show how one is reached, which is what you need when you have to check it, explain it to an employer, a lender or Inland Revenue, or follow the same steps with your own figures.

What one looks like: Two fridges

  1. Fridge A running cost: 400 x $0.30 = $120.00 a year
  2. Over 12 years: $120.00 x 12 = $1,440.00
  3. Fridge A lifetime cost: $1,200.00 + $1,440.00 = $2,640.00
  4. Fridge B running cost: 250 x $0.30 = $75.00 a year
  5. Over 12 years: $75.00 x 12 = $900.00
  6. Fridge B lifetime cost: $1,800.00 + $900.00 = $2,700.00

The efficient fridge costs $60.00 more over its life.

Guides and learning 425 worked calculations

Questions answered in the written guides, from budgeting and KiwiSaver to household spending and employment agreements.

Running a business 281 worked calculations

Margins and break even, cash flow and runway, pricing, subscription revenue, customer value and the true cost of an employee.

Mortgages and lending 132 worked calculations

Repayments and interest, fixed against floating, refinancing and break fees, offset and revolving credit, and what a bank will lend.

Tax on investments and property 95 worked calculations

The bright line test, foreign investment fund rules, tax on interest and dividends, PIE rates and rental income.

Renting, flatting and landlords 84 worked calculations

Rent affordability and flatmates, bonds, rental yield, healthy homes, boarders and the sums a landlord runs.

Benefits, ACC and student support 82 worked calculations

ACC levies and weekly compensation, Working for Families, the Accommodation Supplement, superannuation, student loans and allowances.

Income tax and PAYE 80 worked calculations

Tax codes and secondary tax, PAYE deductions, brackets and marginal rates, refunds, and what actually lands in your account.

Saving and investing 67 worked calculations

Compound interest, managed funds and fee drag, term deposits, shares and dividends, and what a return really nets you.

Budgeting and prices 62 worked calculations

Household budgets, splitting costs, comparing prices and working out what something really costs you.

KiwiSaver 58 worked calculations

Contributions and the government contribution, employer rates and ESCT, funds and fees, first home withdrawals and what happens on death.

GST and business tax 56 worked calculations

GST on a price or a total, provisional tax, company tax, fringe benefit tax, entertainment, mileage and what a contractor owes.

Loans and debt 50 worked calculations

Personal loans and car finance, credit cards, hire purchase and buy now pay later, and the order to clear debts in.

Retirement planning 50 worked calculations

How long savings last, what an income in retirement takes, drawdown rates and the gap between a plan and a number.

Buying a home 46 worked calculations

Deposits and first homes, what a place really costs to own, rates and insurance, building, and buying against renting.

Leave and pay entitlements 31 worked calculations

Annual leave, sick leave and public holidays, parental leave, redundancy and notice, trial periods and how each is paid.

Currency and inflation 26 worked calculations

Exchange rates and the spread a bank takes, what inflation does to a sum over time, and comparing prices across years.

Selling a home 18 worked calculations

Agent commission and what it covers, auctions and marketing, appraisals, settlement, and what is left after a sale.

Every working is taken from the guide that shows it, and that guide is where any rate or threshold is kept current. These are worked examples for education, not advice. Last reviewed 2026-10-04. See also the key points from every guide, every question the site answers, the A to Z of every page and the guides.