The hours already contain the margin
Every hour your team logs updates that project's margin, per client, with no spreadsheet. Cost rate per hour is returned only to Owner and Admin, so members and clients never see internal cost rates, and billable capacity is measured against weekdays rather than calendar days. So what: you catch the overrun in week two, not at invoice time. Honest limit: the numbers come from hours already logged. There is no forecasting and no margin alerting. Where Basecamp stands on this: it sends the data out. In its own words, you can also export the data to bring into an accounting or billing system of your choice. Two systems, one reconciliation, by design.