otd-calculatorlisted

# OTD Calculator > **Caveat**: this skill is one author's playbook + 5-scenario stress test. Verify state fees / CPO terms / EV credits / dealer practices against current sources before quoting numbers to a dealer or making financial decisions. Not tax, legal, or financial advice. > last_verified: 2026-05-18 > Scope: narrow OTD math only. For full negotiation flow see `../orchestrator/SKILL.md`. For state fee data see `../state-fee-lookup/SKILL.md`. ## Core formula (forward: Sale -> OTD) ``` Taxable = Sale + Doc (in most states; CA is a notable exception, see gotchas) Tax = Taxable * (StateRate + LocalRate) OTD = Sale + Doc + Tax + Title + Reg + Other ``` `Other` covers tire/battery/environmental fees, EV reg surcharge, lien recording, and any add-ons that survived F&I. Should be a short itemized list, not a black box. ## Reverse formula (target OTD -> Sale ceiling) Given a target OTD you will pay, solve for the maximum Sale price you can accept: ``` Sale = (TargetOTD - Doc * (1 + Rate) - Title - Reg - Other) / (1 + Rate) ``` Where `Rate = StateRate + LocalRate`. Doc is taxed in most states, hence the `(1 + Rate)` factor on Doc inside the bracket. Verify per-state in the state-fee-lookup skill. ## Trade-in case In states granting trade-in tax credit (most; CA, KY, DC do NOT), trade value reduces the taxable base: ``` Taxable = (Sale + Doc - Trade) ``` Forward with trade: ``` OTD = Sale + Doc + (Sale + Doc - Trade) * Rate + Title + Reg + Other ``` Reverse