When Flat Fees Aren't Flat: Budgeting for Hidden Overtime

I recently tried a new approach to budgeting for my crew on a short film with a tight schedule and even tighter funds. Instead of hourly rates for everyone, I opted for flat daily rates for key creative positions like the DP, Gaffer, and 1st AD, assuming it would simplify payroll and contain costs. What I learned was that 'flat' often isn't truly flat when you're shooting 12+ hour days. The expectation, unspoken but palpable, was that these flat rates still needed to be competitive with what they'd make hourly with overtime, leading to last-minute renegotiations or, worse, resentment that affects morale and performance.

What worked well in theory (simplified budgeting) fell apart in practice. The initial savings I projected were eaten up by needing to offer additional 'prep' days or 'wrap' payments to compensate for the actual time spent, which far exceeded a standard 10-hour day. What didn't work was assuming a flat rate inherently insulated us from overtime pressures; it just pushed those discussions into a gray area of implied expectations rather than clear, line-itemed costs. Next time, I'll bake in an estimated 'overage' or 'extended day' buffer even for flat-rate positions, or clearly define the parameters of the flat rate (e.g., '12 hours max, then hourly OT'). How do others successfully manage the budget realities of demanding schedules with flat-rate crew without eroding goodwill or breaking the bank?