Four inputs, your number. The math is published at the bottom of the page.
Leak = referrals/month × 12 × close rate × avg deal size × leakage rate. Leakage rates are derived from operator interviews: spreadsheet 18%, CRM notes 12%, memory 35%, no system 45%. These represent revenue from referrals that were made but never properly tracked, attributed, or followed up, resulting in lost deals that would otherwise have closed.