How do I set my default tax rate, overhead and margin?

Tax rate and project overhead live at Settings, Workspace, Financials (/settings/workspace/financials). The default profit margin lives at Settings, Workspace, Estimates (/settings/workspace/estimates). All three seed a new estimate. None of them changes an estimate that already exists.

Default tax rate. A single percentage applied to new estimates, invoices and orders. Leave it blank for no default, which means new documents start at zero. If a project has a location with its own rate, the location wins. That chain is the subject of why is the tax rate on my estimates zero.

Project overhead. A percentage that funds your indirect costs (office, admin, insurance, vehicles) by adding a synthetic cost to every project's budget. You also choose how it is calculated: percent of project revenue takes the same cut off the top of every job, while percent of project profit scales with revenue minus direct cost and is gentler when margins come in thin. Commissions on profit are calculated after overhead is taken out. Set it to 0 to start every project with overhead off. Either way, any project can adjust or disable it on its own Budget tab.

Default profit margin. Applied to each section of a new estimate. It sits on the Estimates page alongside the expiration window and the disclaimer, and a location can override it.

Two permission notes. The tax rate and the profit margin follow the ordinary "Manage workspace settings" permission. Project overhead has its own key, because it lands on every project's budget and a workspace admin who should not touch the formula should not be able to. So the two halves of the Financials page can be editable for different people. See who can change workspace settings.

The Estimates page also carries the expiration window, covered in how to change how long estimates stay valid.