Free tools
Free Financial Calculators
Updated 27 September 2026 · 4 min read
Most money decisions come down to a handful of sums: what will this cost each month, what will it cost in total, and what’s left after tax? KitWren’s financial calculators answer those questions quickly, show the working, and don’t ask for your email address. They’re for general information — a way to understand the numbers before you talk to a lender, employer or adviser.
Open the free Mortgage CalculatorBorrowing
Home loans
- Mortgage Calculator — repayments, total interest and a year-by-year schedule. Choose monthly, fortnightly or weekly repayments, and add an extra repayment to see the interest and time it saves.
- Mortgage Affordability Calculator — an estimate of how much you could borrow from your household income, expenses, debts and deposit, plus the property budget that implies.
The mortgage repayments guide explains the formula and compares 25- and 30-year loans.
Personal and car loans
- Loan Calculator — repayments, total interest and the full cost of a personal loan, including fees.
- Car Loan Calculator — car finance with a deposit, trade-in, fees and an optional balloon payment at the end.
Worked example: a $20,000 personal loan
| 5 years at 6% | 3 years at 6% | 5 years at 9% | |
|---|---|---|---|
| Monthly repayment | ≈ $387 | ≈ $608 | ≈ $415 |
| Total interest | ≈ $3,199 | ≈ $1,904 | ≈ $4,910 |
| Total repaid | ≈ $23,199 | ≈ $21,904 | ≈ $24,910 |
Two lessons from one table: a shorter term costs more each month but saves about $1,300 in interest; and three percentage points on the rate costs about $1,700 more over five years. Fees, which the calculator lets you add, can change the picture again — which is why lenders in many countries must show a comparison rate or APR.
Saving and growing money
The Compound Interest Calculator shows how a starting balance and regular contributions grow, with a choice of compounding frequency, contribution timing, yearly contribution increases and an inflation adjustment to show the result in today’s money. The year-by-year table makes it easy to see how growth accelerates in later years.
Pay and tax
- Salary Calculator — convert pay between annual, monthly, fortnightly, weekly, daily and hourly amounts.
- Hourly Wage Calculator — turn an hourly rate into weekly, fortnightly, monthly and annual earnings; useful when comparing casual, contract and salaried roles.
- Income Tax Calculator — estimate income tax and take-home pay for Australia, the UK, the US and New Zealand.
- GST & VAT Calculator — add or remove sales tax at any rate, with 70 countries’ standard rates built in. See how to calculate GST.
Everyday maths behind the money
- Percentage Calculator — discounts, pay rises and percentage change; the percentages guide explains the formulas.
- Percentage Increase and Percentage Decrease calculators — how much a price or bill has really changed.
Which calculator for which decision?
| You’re deciding… | Start with |
|---|---|
| Whether you can afford to buy a home | Mortgage Affordability, then Mortgage |
| Between two job offers | Salary and Income Tax |
| Whether to finance a car or keep saving | Car Loan and Compound Interest |
| What to charge as a freelancer | Hourly Wage and GST & VAT |
| Whether to consolidate debts | Loan, comparing total cost with your current debts |
Running two calculators side by side is often more useful than one: the repayment on a loan only means something next to the take-home pay that has to cover it.
Getting reliable answers
- Use real figures from a loan offer or payslip rather than round guesses.
- Test a worse case. Try an interest rate two or three points higher than today’s to see whether repayments would still be comfortable.
- Look at totals as well as repayments. The cheapest monthly payment is often the most expensive loan.
- Remember what isn’t included: insurance, account fees, stamp duty and changes to variable rates.
Finally, save your scenarios. A screenshot or a note of the figures you tried makes it much easier to compare offers side by side later — and to ask a lender or adviser sharper questions.
Private by design
The calculators run in your browser. Your income, debts and savings aren’t sent to KitWren or shared with lenders, and there’s no sign-up. The results are general estimates based on the figures you enter, not financial advice; for decisions about your own situation, speak to a licensed adviser or your lender.