Awaiting input
Fill in the fields and press Calculate. Your result appears here and stays in view as you scroll.
The guide
Understanding the Retirement
Project a retirement balance from today’s savings and monthly contributions, then see the income it could support.
What each input means
The calculator asks for 6 pieces of information. Every field is validated before the maths runs, so an impossible value is refused rather than quietly producing a wrong answer.
| Input | What it asks for | Example |
|---|---|---|
| Current age | A number in years, at least 16 and no more than 90. | 35 years |
| Retirement age | A number in years, at least 30 and no more than 95. | 65 years |
| Super or savings now | The balance already set aside for retirement. | 50000 |
| Monthly contribution | What you add each month, including employer contributions. | 800 |
| Expected annual return | A balanced fund has historically returned 6–8% before fees. | 7 % |
| Expected inflation | Used to restate the balance in today’s dollars. | 2.5 % |
A worked example using the default inputs
With current age of 35 years, retirement age of 65 years, super or savings now of 50000, monthly contribution of 800, expected annual return of 7 %, the calculator returns $1,381,802 in 30 years.
| Result line | Value |
|---|---|
| Projected balance at retirement | $1,381,802 in 30 years |
| Starting balance | $50,000 |
| Total contributions | $288,000 |
| Investment earnings | $1,043,802 |
| Balance in today’s dollars | $658,764 |
| Sustainable monthly income at 4% a year | $4,606 |
The same arithmetic runs whatever you type into the form above, so you can reproduce any figure by matching the inputs listed here.
How this is calculated
Balance = P × (1 + i)ⁿ + C × ((1 + i)ⁿ − 1) ÷ i, where i is the annual return ÷ 12, n is months to retirement and C is the monthly contribution.
Working values are kept at full precision and rounded only for display. Impossible dates, zero denominators, negative amounts where they make no sense, and out-of-range values are rejected before any result is shown.
The methods behind these money tools
Almost everything in this section is one of six calculations. Once you know which one a tool is running, the result stops being a black box: you can check it roughly on paper, and you can see which input is doing the work.
| Method | The arithmetic | Where it is used |
|---|---|---|
| Amortising payment | PMT = A × i ÷ (1 − (1 + i)⁻ⁿ) | Mortgage payment, loan payment, auto loan, debt payoff |
| Compound growth | FV = PV × (1 + r)ⁿ + PMT × ((1 + r)ⁿ − 1) ÷ r | Compound interest, investment, retirement, savings goal |
| Simple interest | I = P × r × t | Interest calculator |
| Implied rate | The payment equation solved numerically for the rate | Interest rate |
| Net versus gross | Gross = net × (1 + rate); net = gross ÷ (1 + rate) | GST and VAT, US sales tax |
| Progressive bands | Tax = the sum of each band × its rate, less credits | Income tax and take-home pay |
A is the amount borrowed, i the interest rate per period, n the number of payments, r the rate per period, PV the present value and PMT a regular contribution.
Two conventions matter more than any formula. First, the rate and the period must match: a 6% annual rate over monthly payments is 0.5% per month and 360 periods, not 6% per period. Second, money paid later is worth less than money paid now, which is why an amortising loan charges interest on the opening balance of each period rather than on the average balance.
Nominal and real returns are different things. A 7% return with 3% inflation buys roughly 3.9% more each year, not 7%: real rate ≈ (1 + nominal) ÷ (1 + inflation) − 1.
Two worked examples from this section
These scenarios use the same arithmetic as the tools above, so you can follow the numbers from input to result and then repeat them with your own figures.
A 30-year mortgage of $600,000 at 6.1%
The monthly rate is 6.1% ÷ 12 ≈ 0.5083% and there are 360 payments. Feeding those into the amortising payment formula gives a fixed instalment of about $3,636.
- Monthly principal and interest
- ≈ $3,636
- Total repaid over 30 years
- ≈ $1,308,900
- Interest paid in total
- ≈ $708,900
- Share of the total that is interest
- ≈ 54%
Notice that more than half of everything paid is interest. That is the single most useful fact a mortgage calculator produces, and it is why a small change in rate or term moves the total so much more than it moves the monthly figure.
Adding and removing 10% GST on $250
Adding tax is a multiplication; removing it is a division by the same factor, never a subtraction of the same percentage. Subtracting 10% from a GST-inclusive price gives the wrong answer because the tax was charged on the smaller, exclusive amount.
- $250 plus 10% GST
- $275.00
- GST component
- $25.00
- $275 with GST removed (275 ÷ 1.1)
- $250.00
- The common mistake (275 − 10%)
- $247.50 — too low
The same split works for any rate: divide by one plus the rate to go backwards. For 15% VAT, divide by 1.15; for 18% GST, divide by 1.18.
Assumptions behind every finance figure
Results are computed in exact arithmetic and only rounded for display, so a payment shown as $2,413.65 comes from the unrounded monthly rate rather than from a rounded one. Where a calculator compounds, it compounds at the frequency you choose; where it amortises, it assumes payments land at the end of each period unless the tool says otherwise.
Tax and contribution rates are the legislated rates for the tax year noted in each tool. They change, sometimes retrospectively, and none of these tools can see your personal circumstances: deductions, offsets, salary sacrifice, HELP or student loan balances, private health cover, investment losses, provincial or state tax, and treaty arrangements are all outside the model.
- Lenders and tax offices round differently from us, and they use daily interest, fees and assessment rules that a formula cannot reproduce. Expect small differences from an official statement.
- Nominal returns are not real returns. A 7% return with 3% inflation buys about 3.9% more each year, not 7%.
- Every figure is a planning estimate. For a decision with money at stake, confirm it with the lender, the tax office or a licensed adviser.
Sources and further reading
Reviewed 4 November 2026 · CalcFlow editorial
Common questions
Frequently asked
What return should I assume?+
Use the long-run return for your fund mix after fees. Assuming 10% flatters any plan; assuming 4% pushes saving rates that are hard to sustain. Running the number at two rates is more useful than one precise guess.
Is the 4% rule reliable?+
It comes from US historical data over 30-year retirements and is a reasonable first estimate. Local tax, age pension rules and healthcare costs change what it means for you.
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