Imagine we have an inventory management system. It contains a form where the user can fill in a placed order. The order has some properties like:

  • Date
  • Supplier
  • User who ordered it
  • Total price
  • VAT (tax) in percentage
  • Tax to pay in money

On the right side of the form, there's a section (actually another form) to add products to the order. The user fills in the order properties (see bullet points above), and adds products to the order.

The total price of the order should just be the sum of the prices of all products added to this order. So, its value could be updated with the correct total price when the list of added products changes. At the same time this field must stay editable, because in some circumstances the user must be able to change the total price, whatever the actual total price of the products is. The same thing applies to the tax percentage and tax in money fields. They must be automatically filled with the correct value based on default circumstances so the user has to type in less fields and can leave them with their automatically populated values.

Of course it is contradictory: on the one hand the fields should get filled with a caculated value while the user is busy in the form. On the other hand the user must be able to just change the value, without the problem that the user value is overwritten each time the form recalculates and fills the automatic fields.

I was thinking of a calculate button or something, but this seems not very clean to me. Goal is to make the form as smart as possible, and have the user to type, think and calculate as less as possible.

Mockup: Mockup image

  • Can you post a mock of this so we can see what you're working with? It's hard to get context without it.
    – Mike M
    May 15, 2019 at 13:30
  • Why is the total price entered manually? There should be no need for that.
    – Ren
    May 16, 2019 at 3:33
  • Because sometimes there's a discount. But making a second step or form to enter the discount would be complicated. Because discounts are often calculated in variuos ways, like percentage on one product, percentage on total price, conbination of both, discount in absolute amount of money, discount by rounding the price down, discount by not counting a product, discount proportional to ordered quantity... May 16, 2019 at 9:49
  • Since Discount is the variable here, first recommendation would be to have a manual input option for Discount, instead of Total Price. If Discount is automatically generated that should still be visible to provide clarity on the price. Instead of automatically generating Discount values, how about having an option called 'Check available discount' so that the user can opt to have the discount. True they may miss if they don't opt.
    – Ren
    May 16, 2019 at 10:08

1 Answer 1


In my experience, I've seen forms like this where the discount is another added line item (as if it were another product). So the product would say "Discount" and the price would be some negative value "-10%" or "-$10". Therefore the only manual field would be the discount "price" and everything else would auto-calculate.

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