---
title: "Costs toggle"
description: "The costs toggle decides whether a backtest's results include trading costs, slippage and financing, or are shown gross of them — no re-run needed."
canonical_url: "https://fincanva.com/docs/backtesting/costs-toggle"
last_updated: "2026-09-04"
md_url: "https://fincanva.com/docs/backtesting/costs-toggle.md"
---

# Costs toggle

The costs toggle is the [simulation assumption](/docs/backtesting/simulation-assumptions) that decides whether a backtest's results include trading costs and financing, or are shown gross of them. In the app it is the switch labelled **Costs & interests**, described as "Trading costs, financing & interest" and shortened to "Costs" in the assumptions summary. It changes what the *same run* is showing, not the strategy itself.

**Also seen as:** Costs & interests, Costs

## What does turning costs on change?

Turning **Costs & interests** on deducts every modelled cost of trading and financing from the run you are looking at. Three components get wired in:

- **[Transaction cost](/docs/backtesting/transaction-cost)** — a flat fee charged once per trade execution.
- **[Slippage](/docs/backtesting/slippage)** — a proportional cost on each fill, for the gap between the quoted and the filled price.
- **[Interest-rate markups](/docs/backtesting/interest-rate-markups)** — the financing cost of borrowing for leverage or for shorting, charged as a spread over a reference rate.

With the toggle off, all three are zero: the results assume trading and financing were free.

## Defaults in Fincanva

- **Trading costs are not included on the Free plan.** On Free the assumption stays off and the toggle cannot be turned on, so a Free backtest is always a costless one; Starter, Advanced, Ultimate and Professional all include it. See [what each plan includes](/docs/account-security/what-each-plan-includes).
- **Costs & interests is off by default**, so the figures you meet first are gross of costs and financing.
- Flipping it switches the displayed result immediately, with no new run — every combination is pre-computed when the strategy runs (see [simulation assumptions](/docs/backtesting/simulation-assumptions)).
- It moves every number derived from the equity curve, not only the cost lines: total return, annualized return, the monthly figures and the risk metrics all change.
- What it deducts shows up as its own bands in the [P&L breakdown](/docs/analysis/p-l-breakdown) — "Costs" and "Interest paid".
- The two [interest-rate markups](/docs/backtesting/interest-rate-markups) are saved settings you can edit, separate from the toggle that switches them in or out; the per-trade fee and the slippage fraction are fixed platform assumptions with no setting in the app.
- The Holdings view does not follow this toggle: it always reports with costs off, one of its [Holdings forced assumptions](/docs/backtesting/holdings-forced-assumptions).

## Worked example

One run, viewed twice. With **Costs & interests** off the run shows a total return of +42.0%. Flip it on and the same run shows +38.6%: the 3.4pp difference is the trading fees, slippage and financing the strategy would have paid over the period. Nothing about the strategy changed and no new backtest ran — you switched from the gross view to the after-cost view of the identical run. How wide the gap is depends on how much the strategy trades: one that rebalances monthly pays the per-trade fee far more often than one that holds for years.

*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).*