Can I apply a discount to just one line, or only to the whole invoice?

Both. Kliently lets you set discounts and tax per line or per invoice, with live totals that update as you type. So you can knock 10% off a single line item, or apply one discount across the entire invoice — whichever matches how you quoted the work.

The same flexibility applies to tax: per line when different items are taxed differently, or per invoice when one rate covers everything. Because totals recalculate live, there's no mental math and no risk of a stale subtotal going out to a client.