Can we add our own terms and condition to estimate and invoice ?

Hi accounting555,

Welcome to the Community! QuickBooks Online offers a flexible program that allows you to customize your invoices so they stand out to your customers. I'll be happy to show you how to add your terms and conditions to your estimate and on your invoice. 

You can add a custom message on your invoice  by clicking on the Gear icon > Custom Form Styles > open the invoice/estimate template in question > navigate to the Content tab > from here click on the bottom part of your invoice on the right side > you'll now see an option that allows you to add a Message to customer on. I encourage you to add your terms and conditions here and make sure to save your changes once you're done. 

Here's a helpful article that shows you how to: 

Customize invoices, estimates, and sales receipts in QuickBooks Online. 

Let me know if this info helps by leaving a comment below. I'll be one message away in case you need anything else.