Enter your figures.

You'll need your opening and closing stock values, purchases and total sales for the same period, usually one week.

Stock value at the start of the period.
Stock value from your latest count.
Stock purchased during this period.
Revenue after discounts and all other sales deductions have been accounted for.
Discounts already deducted from the sales figure above. Do not include them twice.
Opening stock, closing stock and purchases must be entered excluding recoverable VAT. If your sales include different VAT rates, use your actual VAT-exclusive sales figure. Discounts must use the same VAT basis as sales.

A little more information.

These details are optional, but they'll help make the results more useful.