Bookkeeping Calculator

Present Value Calculator

Enter a future target, an interest rate and a time frame to find out how much you would need to invest today.

Bookkeeping Formula Reference

Every formula used by these calculators. They match the FNSACC323 Perform financial calculations unit.

Tax
GST: Add
Price inc GST = Price ex GST × 1.1
e.g. $100 × 1.1 = $110
GST: Remove
Price ex GST = Price inc GST ÷ 1.1
e.g. $110 ÷ 1.1 = $100
GST: Find Amount
GST = Price inc GST ÷ 11
e.g. $110 ÷ 11 = $10
Business
Markup
Selling Price = Cost + (Markup% × Cost)
e.g. Cost $50, Markup 20% → SP = $50 + ($50 × 0.20) = $60
Profit Margin
Selling Price = Cost ÷ (1 − Margin%)
e.g. Cost $50, Margin 20% → SP = $50 ÷ 0.80 = $62.50
Sales Commission
Commission = Rate% × Total Sales
e.g. $10,000 sales at 5% → Commission = $500
Simple Interest
Simple Interest
Interest = Principal × Rate × Number of Periods (T)
I = P × R × T
e.g. $300 at 2% for 1 year → I = $300 × 0.02 × 1 = $6
Total Value / Total Repayable
Total = Principal + Interest
e.g. $300 + $6 = $306
Compound Interest
Future Value (Compound)
FV = PV × (1 + i/n)^(n×t)
PV = present value, i = annual rate, n = periods/year, t = years
Present Value
PV = FV × (1 + i/n)^(−n×t)
How much to invest now to reach a future target
Loan Repayment
Repayment = P × [rp × (1 + rp)^N] ÷ [(1 + rp)^N − 1]
rp = rate per period, N = total periods
Depreciation
Straight Line: No Residual
Depreciation = Total Cost ÷ Effective Life
e.g. $11,000 ÷ 5 yrs = $2,200 per year (same each year)
Straight Line: With Residual
Depreciation = (Total Cost − Residual) ÷ Effective Life
e.g. ($11,000 − $1,000) ÷ 5 = $2,000 per year
Diminishing Value: Rate
Rate % = 200% ÷ Effective Life
e.g. 200 ÷ 12 yrs = 16.67%
Diminishing Value: Depreciation
Depreciation = Rate % × Carrying Amount
Applied to the reducing book value each year, bigger early, smaller later

GST Calculator (Australia)

GST Rate: 10%
$

Results

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Markup / Profit Margin

Markup calculates profit as a percentage of the cost price. Profit Margin calculates profit as a percentage of the selling price.

SP = Cost + (Markup% × Cost)
$
%

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Sales Commission

Commission = Rate% × Total Sales
$
%
$

Results

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Break-Even Point

Units = Fixed Costs ÷ (Price − Variable Cost)

Fixed Costs stay the same no matter how much you sell (e.g. rent, insurance). Variable Cost is what it costs to make or deliver one single unit (materials, packaging, per-item shipping) — it goes up and down with sales, unlike fixed costs. Selling Price is what you charge per unit.

$
$
$

Results

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Simple Interest

I = P × R × T
$
%

Results

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Compound Interest

FV = PV × (1 + I)ᴺ
$
%
$

Results

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Present Value

PV = FV × (1 + I)⁻ᴺ
$
%

Results

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Depreciation

Depn = (Cost − Residual) ÷ Life
$
$

Results

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Time to Decimal

Decimal Hours = Hours + (Minutes ÷ 60)
hrs
min

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Pay Calculator (Before Tax)

Gross Pay = (Rate × Ord. Hours) + (Rate × OT × OT Hours)
$

Results

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GST / VAT / Sales Tax Calculator

Rate: 15%
%
$

Results

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The present value formula

PV = FV × (1 + i/n)^(−n × t)

Present value runs compound interest backwards. Instead of asking what today’s money will grow into, it asks what a future amount is worth today.

Example. You need $20,000 in 5 years and can earn 4% a year compounded monthly.

PV = $20,000 × (1 + 0.04 ÷ 12)^(−60) = $16,380.06. Invest that today and it grows to $20,000.

What it is used for

A higher interest rate or a longer time frame both lower the present value, because the money has more room to grow. To go the other way, use the compound interest calculator.

Frequently asked questions

What does present value mean?

The amount that would need to be invested today, at a given interest rate, to grow into a specified future amount.

Why is present value less than future value?

Because money invested today earns interest. The gap between the two is the interest earned over the period.

What interest rate should I use?

Use the rate you could realistically earn on the money over that time, such as a term deposit or savings account rate.

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