The calculation of values in a document is based on the values of existing products / services. Upon issuing a document, either the initial or the total price of products / services is known to us, along perhaps with a discount or tax rates we may wish to apply to each product / service separately. The item calculation method can be applied **per document** or for **all invoices **by the "Application settings".

To select how you want the calculations to be done in a document during processing, click on the blue “gear” icon in the right top of the Products / Services section. Then, you must choose if the calculations will be based on the initial or total value - as shown in the following picture - and click OK:

As an example, initially we will calculate the values for a document including a single product / service, multiplied by 10, based on the total price and then calculate the values of the document for the same product / service in the same amount, but based on the initial value.

**Value calculations based on totals**

Let us assume that the product’s total value is known, equal to 9,99 and wish to apply a VAT rate of 20%. The value of this particular product / service is displayed on the image below.

Since you wish the product / services quantity to be 10, the total value of the document occurs as follows:

**Value calculations based on initial value
**

In the above scenario values were calculated based on the totals values of products / services. In some cases, however, the product / services initial value is known to us.

Let us assume you wish to calculate the last document's total amount based on the initial values of product / services. After you select the initial value calculation method, as described above, the new values are automatically calculated upon the document. In the image below the new values can be seen, as occurred based on initial value.

The document’s total amount is now calculated as total initial value of existing products / services (remember that unit's initial value is 8,325), plus taxes.

**Notice** how out of two, seemingly identical, product / services unit values occurs a difference on the document’s total amount by choosing different calculation methods.