Brightpearl calculates tax per item and then multiplies it by the item quantity.
Some other systems, such as Sage, Xero and QuickBooks first multiply the item net price by qty, and then calculate tax on the total - otherwise known as line level tax calculations.
Both UK and US tax rules allow tax to be calculated in either way. Both methods are perfectly acceptable, but it means that when comparing Brightpearl invoices to invoices from other systems, the tax amounts may not match exactly - especially when you have low priced items.
Most of the time, for most merchants, all software will show exactly the same values.
Here's how Brightpearl calculates order totals. The reason we do it this way is to support direct entry of prices inclusive of tax, for all item values and quantities. For this demonstration item price of 1.95, to get an order total of 1.95 we need to perform additional steps.
For the same item, if we use an example line based calculation, entering an item price including tax as 1.95 gives an order total of 1.96 ... more than the original item cost.
Here's a further example of how order totals can vary slightly when quantities are high. If charging a retail price of 0.28 (inc tax), and selling 1000 items, one would expect the order total to be 280.00.
Firstly using item-level calculations (as per Brightpearl):
And the same 1000 items using line-level calculations:
Tax rates at an order level are not always exact
For the item-based example of 1000 items, the order tax amount of 46.70 is not in fact exactly 20% tax, it's 20.017%
The same principle applies if you sell low price items; the first example of 0.33 tax on an item price of 1.63 gives an effective tax rate of 20.25% - taking the line level example. As soon as you have to round order totals to 2 decimal places (because you can't pay fractions of a penny), there will be some deviation from the exact tax rate.