I worked in commercial real estate. Not as a developer — as an operator. Every month, someone on the team had to sit down and manually calculate billing schedules. Every contract had a free rent period, a rent escalation clause, a non-standard start date. Usually all three. You’d open Excel, start calculating day counts, apply the escalation rate, handle the stub period at the beginning, handle the one at the end. It took hours. It was error-prone. And when you got it wrong, the tenant pushed back. I got tired of it. I knew how to code. So I built something. What the problem actually looks like A real contract: Lease starts March 15 Free rent for the first 2 months From month 3: base rate kicks in From month 13: base rate × 1.05 (anniversary escalation) Billing anchor is the 15th of each month Now generate a clean monthly billing schedule for 3 years. Every period needs the right dates, the right applied rate, the right amount. The stub periods at the start and end need to be handled correctly.…