Somewhere in your practice there is probably a spreadsheet called something like PTO Tracker FINAL v3. It has a row per employee, a balance column, and a quiet history of being wrong. Not dramatically wrong, wrong by fractions of hours that nobody audits until an RBT gives notice, HR calculates a payout, and the number doesn't match what the employee believes they earned. Now it's a dispute, and depending on your state, a legal one.
PTO seems like simple arithmetic, which is exactly why it goes wrong. The failure cases live in the edges, and ABA staffing, hourly RBTs, high turnover, variable hours, tiered tenure benefits, is made of edges.
Mid-period hires and exits. If accrual is 5 hours per month and someone starts on the 19th, what do they earn in month one? Pro-rated by calendar days? Working days? Nothing until the first full period? All are defensible policies, but a spreadsheet applies whichever one the person editing it remembered that day, and applies it inconsistently.
Tier changes. Your policy says 10 days a year for the first two years, 15 after. An RBT crosses the two-year mark on March 7th. Their March accrual should be split across two rates. Most spreadsheets just flip the rate in April, a small underpayment, times every employee who ever crosses a tier, forever.
Carryover caps. December 31st arrives and unused balances above the cap should expire, unless your state treats earned PTO as wages that can't be forfeited, in which case caps work differently (accrual pauses at a ceiling rather than balances expiring). If your tracker just resets numbers in January, you may be quietly violating state wage law.
Negative balances and retro adjustments. Someone borrows two days against next month, then resigns. Someone's approved request gets cancelled after the accrual ran. A timesheet correction changes hours-worked-based accrual three periods back. A single balance cell can't represent any of this honestly.
Because in ABA, a PTO error isn't only a payroll problem, it's a schedule problem. An RBT out on approved leave means sessions to cover, authorizations still burning, and families to notify. When PTO lives in a spreadsheet and scheduling lives in your practice platform, that connection is manual, and late-notice absences become lost revenue. When they live in one system, an approved time-off request immediately surfaces the coverage gap on the schedule, and payroll picks up the paid hours without re-keying.
That's the argument for treating HR as part of the practice platform rather than a separate subscription: not that spreadsheets can't be maintained, but that PTO, scheduling, payroll, and compliance are one workflow in real life, and software boundaries between them are where the money leaks.
ABAVault™'s leave system is built as exactly this kind of ledger, accrual tiers, carryover rules, mid-period proration, and negative-balance handling, wired directly to scheduling and payroll. It's part of why our accrual engine is one of the most heavily tested pieces of code we ship: a silent bug here would cost a practice real money, so we treat it like billing code.