--- title: Determining When FX Calculations Should Occur | Vibe Accounting in Public - Day 18 description: "Another lesson in building reliable AI for accounting: validating that your FX calculations happen last, every time. Not negotiable." --- [Leapfin Blog ](https://www.leapfin.com/blog) # [Determining When FX Calculations Should Occur | Vibe Accounting in Public - Day 18](https://www.leapfin.com/blog/determining-when-fx-calculations-should-occur-vibe-accounting-in-public-day-18) Written by [Erik Yao, Co-Founder & CTO at Leapfin](https://www.leapfin.com/blog/author/erik-yao) | Oct 5, 2025 7:15:00 AM Day 18 of Vibe Accounting: [Luca](https://www.leapfin.com/luca-ai) Invents Money Out of Thin Air 💸 and learns you can't manifest currency gains through sheer confidence. So here's a fun Monday: reviewing our AI agent's work and notice we're booking $2.3M in FX gains while reconciling last month. First thought: "we're rich???" Second thought: "we are so not rich." ## The Problem [Our AI agent](https://www.leapfin.com/luca-ai) was confidently calculating foreign exchange gains and losses... before the actual currency conversions had even happened. It was placing FX calc workflows arbitrarily in the process, assuming all the currency conversion work was already done. Like calculating your profit margin before you've actually sold the product. Cart, meet horse. ## The Fix Giving it a nudge to fix itself wasn't too painful, but we wanted to ensure this never happens again. We have a two-pronged approach: Workflow positioning: Train the agent to always place FX calculations as the terminal stage. Not negotiable. Last thing, every time. Currency validation: Before any FX calc runs, validate currencies actually make sense. If everything's already in the same currency, skip it. Don't hallucinate exchange rates. ## The Meta-Lesson Yeah, we have an AI that tried to make us accidental FX millionaires. But catching it reminds us yet again: validation layers aren't optional for AI agents in accounting. It's worth repeating on every post I make. You can't just trust the vibes on financial calculations. The agent's intuition about "FX calculations should happen somewhere" wasn't wrong. But "somewhere" and "at exactly the right time with the right preconditions" are very different. Building AI agents for accounting means teaching them not just WHAT to do, but WHEN and UNDER WHAT CONDITIONS. Also pretty sure [our agent](https://www.leapfin.com/luca-ai) briefly thought it was smarter than the entire forex market. Onwards 🚀 #VibeAccounting ### Read our other Vibe Accounting in Public posts: [Day 19 - Complete Stripe Order-to-Cash and Revenue Recognition Workflow in 5 Minutes](https://www.leapfin.com/_hcms/analytics/search/conversion?redirect=aHR0cHM6Ly93d3cubGVhcGZpbi5jb20vYmxvZy9jb21wbGV0ZS1zdHJpcGUtb3JkZXItdG8tY2FzaC1hbmQtcmV2ZW51ZS1yZWNvZ25pdGlvbi13b3JrZmxvdy1pbi01LW1pbnV0ZXMtdmliZS1hY2NvdW50aW5nLWluLXB1YmxpYy1kYXktMTk%3D&ct=SEARCH&pid=8117914&cid=197594940337&t=dmliZQ%3D%3D&d=www.leapfin.com&c=2&rp=13&ab=true&opcid=&rs=UNKNOWN&hs-expires=1791986986&hs-version=1&hs-signature=APUk-v4z2y2pyzG-xrIzj0IXCkrX_HB-pg) [Day 18 - Determining When FX Calculations Should Occur](https://www.leapfin.com/_hcms/analytics/search/conversion?redirect=aHR0cHM6Ly93d3cubGVhcGZpbi5jb20vYmxvZy9kZXRlcm1pbmluZy13aGVuLWZ4LWNhbGN1bGF0aW9ucy1zaG91bGQtb2NjdXItdmliZS1hY2NvdW50aW5nLWluLXB1YmxpYy1kYXktMTg%3D&ct=SEARCH&pid=8117914&cid=197588999857&t=dmliZQ%3D%3D&d=www.leapfin.com&c=2&rp=5&ab=false&opcid=&rs=UNKNOWN&hs-expires=1791986891&hs-version=1&hs-signature=APUk-v57oKG6DywSxDXtyvzTVgauwBvXqw)  [Day 17 - 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