The cost side: what you paid and when
Every item needs a purchase record made on the day you buy it. Not the day it sells, and not the weekend after a release when you are trying to remember which card paid for what.
- Item, size or variant, and quantity.
- Retailer and order number.
- Date ordered and the total paid, including delivery.
- Which card or account paid, so a refund can be matched later.
- The order confirmation or receipt, kept somewhere you can find it.
Where the stock is right now
Between paying and selling, an item is in one of several states: ordered, shipped, delivered, listed, sold, sent to the buyer, returned. Most lost money hides in the gaps between those states.
A parcel that never arrived is a claim with a deadline. A pre-order that has not charged yet is money you need in the account next month. A return you posted back is a refund somebody owes you. If your records only have a row for things that sold, none of these are visible.
The sale side: what the buyer paid
Record the sale price, the date, the platform and the buyer's order reference. If the buyer paid for postage, note that separately from the item price, because fees are often charged on the total.
Private sales count too. A cash sale at a card show or a bank transfer from someone in a group chat is still a sale, and it is the kind that gets forgotten by January.
Fees, per platform and per sale
Fees are where estimated profit and real profit part company. Each marketplace charges differently, some take a cut of the postage as well as the item, and payment processing can be a separate line. Promoted listings and authentication services add more.
Record the actual fee on each sale instead of applying a rough percentage across the lot. A rough percentage is usually wrong in the same direction: it makes you look more profitable than you are.
Postage, packaging and other expenses
The label you bought, the box, the tape and the bubble wrap all come out of the sale. Record postage per sale and buy packaging in bulk as a general expense.
Then there is everything that is not tied to one item: subscriptions, software, storage, mileage to the Post Office, a label printer. These are easy to ignore and they are real costs. Keep the receipt with the entry.
Profit: the number that ties it together
Profit per item is the sale price, minus fees, minus postage and packaging, minus what the item cost you. Profit for the month is the total of those, minus your general expenses.
Two more numbers are worth watching. One is money tied up in unsold stock, because a great profit figure is not much use if all of it is sitting in boxes. The other is money owed to you: refunds, returns and cancelled orders that have not come back yet.
Why spreadsheets break
A spreadsheet is the right place to start. It is free, flexible and everyone knows how to use one. It tends to fail in the same few ways once volume picks up.
- It only knows what you type. On a busy week the typing falls behind, and a record that is two weeks out of date answers nothing.
- One row cannot be several things. An item is ordered, then in transit, then stock, then sold, then maybe returned. People end up with a tab for each and no link between them.
- Fee formulas go stale. Platforms change their fees, and nobody goes back to fix the formula in last year's sheet.
- It is not connected to anything. The tracking number lives in an email, the refund lives in a banking app, and the sheet has neither.
- It is awkward on a phone, which is where you are when the parcel arrives or the sale comes in.
- One bad sort or one overwritten cell can scramble months of work without anyone noticing.
What to use instead
The fix is less about the software and more about the habit: record at the moment something happens, in one place, with the status of every item visible. If a spreadsheet still gives you that, keep it.
When it does not, move to something built for the job. Minted members keep inventory, expenses, refunds and pre-orders together, see profit and loss as they go, and have their parcels on a tracker for every UK courier next to the stock they belong to. For a plain-English explainer of how HMRC's guidance treats reselling, read do you pay tax on reselling in the UK? Nothing here is financial or tax advice, and Minted does not calculate or file tax.