You send out an affiliate payout on day one of month four. The spreadsheet says $47,230. Your accountant checks Stripe and finds $42,950. The gap is $4,280—nine percent of what you promised to pay. You dig back through three months of data and find rounding errors, missed refunds, partial refund tax splits, and currency conversion orphans. Each one is small. Together, they've eaten your payout reserves. This is not a rare edge case. It happens to every affiliate program that relies on spreadsheets past month three. The math itself is sound. The tracking isn't. Why the drift starts small and compounds Affiliate payouts begin cleanly. Month one: ten affiliates, $5,000 in commissions, one spreadsheet. Payouts are accurate. By month four, you have forty affiliates, $50,000 in monthly volume, and three people touching the spreadsheet. The drift doesn't come from intentional error. It comes from these five sources: Rounding variance. One affiliate earns $47.335 in commission. Your payout system rounds to $47.33. Stripe records $47.335. Over forty affiliates per month, you lose $8–15 in rounding direction alone. Refund lag. A customer pays on day 15. Affiliate earns commission on day 16. Customer requests a refund on day 25. You process the refund on day 26 but don't reverse the affiliate commission until next month's audit. Now the affiliate was paid for work that didn't stick. Partial refunds split wrong. A $200 order includes $50 in shipping. Customer refunds only shipping. Your spreadsheet either refunds the full commission or none. Stripe shows a partial reversal. You're out by the commission on $50. Currency conversion ghosts. An affiliate in EUR earns €45 on a USD transaction. Your spreadsheet converts at today's rate: €45 = $49.50. Stripe converts at the transaction rate from last week: €45 = $48.90. The payout was $48.90. Your spreadsheet shows $49.50. Every international affiliate adds 0.5–1.2% drift per month. Chargeback reversals not tied to affiliate records. A customer disputes a $500 transaction. Stripe reverses it in a bulk chargeback file. Your spreadsheet doesn't auto-map chargebacks to the original affiliate commission. You either double-pay or skip them—and only find out during reconciliation. None of these errors is large enough to catch in week one. By month three, they've accumulated to $1,200–$2,100 across your affiliate base. By month four, when you run a full reconciliation against Stripe, the spreadsheet total is 8–12% below reality—or above it, if refund lags have been buried. Real data: six months of drift mapped Here's what a clean affiliate program audit looks like across six months: Month Spreadsheet Total Stripe Billing Actual Drift % Primary Cause Month 1 $12,450 $12,475 0.2% Rounding Month 2 $24,890 $25,140 1.0% Refund lag Month 3 $38,320 $38,950 1.6% Partial refunds + EUR conversion Month 4 $51,240 $55,890 8.3% Chargeback reversals unmapped Month 5 $63,100 $68,500 7.9% Cascading refund lag + chargebacks Month 6 $76,850 $86,120 10.7% All of above + currency backlog The first two months look good because volume is low and nothing has time to compound. Month three is where drift becomes visible. By month six, your spreadsheet underpays by over $9,000—money you promised your top affiliates. The moment you hit month four and discover an 8% gap, you have three choices: manually audit every transaction (30–40 hours), write a script to pull Stripe raw data and match it line-by-line (15 hours upfront, 2 hours per month), or automate the entire process and never face it again. The core math: where each percentage point leaks Let's break down a realistic month with $50,000 in affiliate payouts and show exactly where the drift hides. Rounding: 0.15% 45 affiliates, average payout $1,111.11 each. Your system rounds down to the nearest cent. Over 45 people, rounding costs $0.23–$0.38 per payout. Multiply by 45 and you lose $10–$17 per month, or $75/year. It's not nothing, but it's table stakes. Refund lag: 0.8–1.2% $50,000 in payouts means roughly $250,000 in gross sales (at a 20% commission rate). Of those, 8–12 customers will request refunds. The average refund is $150. Affiliate earned 20% = $30 commission. Your spreadsheet usually records refunds the day after you process them in your payment gateway. Stripe records them immediately. Over 30 days, 8–10 refunds stack up unreversed in your payout number. That's $240–$300 in overstated payouts, or 0.48–0.6%. Partial refunds and tax splits: 1.5–2% Of those refunds, about 30% are partial. A $200 order refunded at $50 shipping. Your system either claws back full commission or none. Stripe claws back proportional commission ($12.50 if the full commission was $50). Over 10 partial refunds per month at an average $75 shortfall, you're at $750—1.5% of payout. Currency conversion: 0.6–1.1% If 15% of your affiliate volume is international, you're converting EUR, GBP, JPY, or SGD. Your spreadsheet may convert at today's rate or at average month rate. S