---
title: "Transaction cost"
description: "Transaction cost is the flat fee Fincanva charges once per trade execution in a backtest — a fixed amount per fill, not a percentage and not a per-share charge."
canonical_url: "https://fincanva.com/docs/backtesting/transaction-cost"
last_updated: "2026-07-25"
md_url: "https://fincanva.com/docs/backtesting/transaction-cost.md"
---

# Transaction cost

Transaction cost is the flat fee Fincanva charges once for each trade execution in a backtest. It is a fixed amount per fill — **not** a percentage of the order's value and **not** a charge per share — so a large order and a small one carry exactly the same fee. It models the commission a broker charges to execute a trade, and it is the fee half of trading costs; the price half is [slippage](/docs/backtesting/slippage), which *is* proportional.

**Also seen as:** transaction fee, commission, brokerage commission, "Trading costs" (the results label).

## How is transaction cost charged?

One execution, one flat fee, added to the cash flow of that execution. Because a buy and a sell are two separate executions, a full round trip on one holding costs the fee twice. Nothing about the fee scales with the order: doubling the size of a trade does not double its fee.

That has one practical consequence worth reading off directly — a flat fee is a **larger share of a small order than of a large one**. The same fee is a rounding error on a 20,000 order and a visible bite out of a 200 one, so it weighs most on strategies that trade small amounts often.

Slippage works the other way round: it is proportional, so it scales with the value traded. The two are separate components and both are switched in by the same [costs toggle](/docs/backtesting/costs-toggle).

## Defaults in Fincanva

- The fee is a flat **1.2 per fill**, in the simulation's base currency.
- It is a fixed platform assumption today — there is no setting in the app for changing the per-trade fee.
- It is charged only when **Costs & interests** is on; with costs off, the modelled transaction cost is zero.
- Every execution counts separately, so the total for a period follows the number of fills, not the amount of money traded.
- In results it is aggregated with slippage: the "Trading costs" figure and the "Costs" column in the positions view carry both.

## Worked example

A strategy holds 10 positions and [rebalances](/docs/backtesting/rebalance) monthly, and each rebalance replaces about half the book — 5 sells and 5 buys, so 10 fills a month, 120 fills over a year. At 1.2 per fill that is 120 × 1.2 = **144** in transaction cost for the year.

What that costs depends entirely on the capital, because the fee does not scale with it. On 10,000 of starting capital, 144 is about 1.4% of capital consumed by fees in one year. On 100,000 running the identical strategy, the same 144 is about 0.14%. Same trades, same fee count, ten times less drag — which is why per-trade fees hit small accounts and high-turnover strategies hardest.

*The figures on this page describe what Fincanva models, not what you should do with your money — see [Is this financial advice?](/docs/investing-theory/is-this-financial-advice#is-this-financial-advice).*