If you work in maritime trade, you handle PDAs and FDAs daily. But if you are new to the industry — or if you are building software for it — the distinction matters more than it appears.

PDA — Proforma Disbursement Account. This is the estimate. Before a vessel arrives at port, the port agent prepares a PDA listing all expected charges: port dues, pilotage, towage, berth hire, agency fees, and any other anticipated costs. The PDA is sent to the ship owner or charterer for approval before the vessel arrives. It is essentially a quote — a detailed projection of what the port call will cost.

The PDA serves two business purposes. First, it allows the principal (ship owner or charterer) to budget and pre-fund the port call. Second, it establishes the commercial terms between the agent and the principal. Once the principal approves the PDA, the agent has authorisation to incur the listed expenses on the principal's behalf.

FDA — Final Disbursement Account. This is the actuality. After the vessel departs, the agent prepares an FDA listing the actual charges incurred. Some charges will match the PDA exactly (fixed fees like agency fees). Others will differ (variable charges like berth hire, which depends on how long the vessel actually stays alongside). Some charges may appear on the FDA that were not on the PDA (unexpected costs like shifting, additional surveys, or canal transit fees).

The FDA is the settlement document. It is the basis for the final payment from the principal to the agent. The difference between the PDA amount (which was pre-funded) and the FDA amount (the actual cost) determines whether the agent owes the principal a refund or the principal owes an additional payment.

Why the distinction matters for software. A system that treats a PDA and an FDA as the same document will fail. They have different workflows, different approval requirements, and different business rules. A PDA can be revised multiple times before approval. An FDA is typically issued once and disputed if the principal disagrees. A PDA may include estimated ranges for certain charges. An FDA must show exact amounts with supporting documentation.

In Tarshix, a PDA and an FDA are linked to the same transaction (the port call) but follow different lifecycle paths. The PDA is created before the vessel arrives, approved by the principal, and used to generate a pre-funding request. The FDA is created after departure, reconciled against the PDA, and used to calculate the final settlement. The system tracks the variance between PDA and FDA automatically — showing the agent exactly where estimates differed from actuals.

This level of domain-specific understanding is why generic invoicing tools fall short. They see an invoice. Tarshix sees a trade workflow with multiple stages, multiple parties, and multiple documents that must reconcile against each other.