Invoice Credit Note Generator
A properly formed credit note, with the reason and the tax credited back.
Invoice Line Item Calculator
Work out one line: quantity, price, discount and tax, with the arithmetic shown.
Quick Tool Overview
The Invoice Line Item Calculator works out one line — quantity, unit price, discount and tax — with each step separate, and solves backwards when three of the four figures are fixed and the fourth is not.
- What it does
- Works out a single invoice line
- You give it
- Quantity, price, discount and rate
- You get back
- Gross, discount, net, tax and line total
- Best for
- Checking a line, or hitting an exact total
About the Invoice Line Item Calculator
One line of an invoice involves four numbers and two rules, and the rules are where it goes wrong. Quantity times unit price gives the gross. The discount comes off that, before tax, because tax is charged on what you actually charged. Tax applies to what is left. Rounding happens at the currency’s own precision.
This shows each step separately, which makes it useful for exactly two things: checking a line on an invoice somebody has sent you, and working out the figure to type when you are building one by hand. Both are far more common than any invoicing software admits.
It also works backwards. Fix any three of the four figures and it solves for the fourth, so you can answer "what unit price gives a line total of exactly £500" without doing it by trial and error — which is a question that comes up whenever a budget is fixed and the quantity is not.
Key features of the Invoice Line Item Calculator
Every step separate
So an error is locatable rather than just present.
Discount before tax
Which is what the law requires and templates forget.
Solves backwards
What unit price gives a line total of exactly £500.
Fractional quantities
2.5 hours and 1.75 metres, to three decimal places.
Inclusive or exclusive
Tax added on, or backed out of a price that contains it.
How to use the Invoice Line Item Calculator
-
1
Enter the quantity and unit price
Fractional quantities are fine — 2.5 hours, 1.75 metres.
-
2
Add any line discount
A percentage or an amount. It comes off before tax.
-
3
Set the tax rate
And say whether the unit price already includes it.
-
4
Read every step
Gross, discount, net, tax and line total, separately.
-
5
Or solve backwards
Fix the line total and it works out the price or quantity that produces it.
Frequently asked questions
Before. Tax is charged on the amount actually charged, so a discounted line is taxed on the discounted figure.
To the currency’s own precision — two places for most, none for the yen, three for the Gulf dinars. Round the line once rather than rounding the components.
Yes, and it often should be. Billing 2.5 hours or 1.75 metres is more honest than rounding up to 3 and 2, and most invoicing conventions allow up to three decimal places on a quantity.
Then the line total is the tax-inclusive figure and the tax is backed out of it rather than added. Switch the tax treatment to inclusive and the maths changes accordingly.
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