The tools below help resellers understand how fees, costs, pricing, and inventory speed affect their listings.
Each tool is designed to clarify a specific structural question. They are deliberately simple. They are not bookkeeping systems, forecasting software, or optimisation dashboards.
These tools are designed for quick operational testing rather than full accounting systems.
If you are unsure where to begin, start with the constraint you are currently facing: fees, margin, pricing, or how quickly inventory is selling
These models explain how individual listings behave financially. The operational side of managing inventory and sales across marketplaces is documented separately.
The software I currently use to manage inventory and sales across marketplaces is explained in my Flipwise review.
Tools Included on This Page
This page currently includes the following working models:
- eBay Fees Calculator (UK) – estimate how marketplace fees affect a single transaction.
- Margin Calculator – calculate true profit after fees, shipping, and operational costs.
- Break-Even Price Calculator – determine the minimum sale price required to avoid loss.
- The 2-Month Rule – test whether inventory is selling fast enough to support stable income.
Each tool focuses on a different structural question inside a reseller business.
How the Tools Work Together
Each tool looks at a different layer of the same system.
The eBay Fees Calculator (UK) explains how money moves inside a single transaction. It clarifies how final value fees, promoted listings, payment processing, and VAT affect what you actually receive.
The Margin Calculator builds on this by incorporating sourcing cost, shipping, packaging, returns, and other operational expenses.
The Break-Even Price Calculator works in reverse by estimating the minimum sale price required to avoid loss.
The 2-Month Rule steps back further. It tests whether inventory is cycling fast enough to stabilise monthly income.
Used together, they answer four structural questions:
- How are fees applied?
- Is this listing profitable?
- What price protects margin?
- Is my capital cycling fast enough?
Clarity at the transaction level supports discipline at the inventory level.
Model first. Adjust second.
Suggested Order for New Users:
- eBay Fees Calculator (UK) – understand fees.
- Margin Calculator – estimate true margin.
- Break-Even Price Calculator – find the price floor.
- 2-Month Rule – assess inventory velocity.
eBay Fees Calculator (UK)
Estimate how marketplace fees affect a single transaction.
This tool models final value fees, promoted listing percentages, payment processing, and VAT on fees. It shows what you actually retain after the sale completes.
Best used before publishing or revising a listing.
This tool explains how fees affect a single transaction, which is the first layer of the reseller model described on this page.
→ Use the eBay Fees Calculator
Margin Calculator
Calculate the true margin of a listing after all direct costs.
This tool incorporates sourcing cost, shipping you pay, packaging, returns, promotion, and fees. It shows net profit and margin percentage based on your actual inputs.
Best used when setting price or deciding whether promotion is sustainable.
This model builds on the fee calculation above and tests whether the listing is structurally profitable.
→ Use the Margin Calculator to model your own listings.
Break-Even Price Calculator
Pricing decisions compound quietly.
This calculator estimates the minimum sale price required to cover product and operational costs after marketplace fees, payment processing, promoted listing percentages, VAT on fees, and expected returns.
It answers two structural questions:
- At what price do I stop losing money?
- At what price do I achieve a target margin?
The goal is not precision accounting. It is disciplined pricing before you publish a listing or upgrade equipment.
This model works backwards from your costs and fees to determine the minimum sustainable price
→ View the Break Even Price Calculator
Assumptions and Notes
The Break Even calculator is designed for quick operational testing rather than bookkeeping.
- Final value fees and payment percentages are calculated on the total amount paid by the buyer, including shipping charged.
- Returns are modelled as a simple percentage of sale price and reduce expected revenue proportionally.
- VAT on fees can be toggled on or off to reflect your situation. Confirm treatment with your accountant if needed.
- Shipping cost, packaging, and other operational expenses are deducted after fees.
- This tool runs entirely in your browser. No data is stored.
If the required break-even price feels uncomfortable, that is useful information. It suggests either sourcing cost, fee structure, or category choice needs rethinking before listing.
The 2-Month Rule
A simple inventory discipline model.
The rule tests whether capital is cycling fast enough to support stable monthly income. It forces a decision: reduce buying, improve sell-through, or adjust pricing.
Best used when cash feels tight but stock levels remain high.
This rule shifts focus from individual listings to the speed at which your inventory converts into cash.