Confirm the cartridge, not just the brand

Use the printer manual or manufacturer's compatibility tool to check the correct cartridge code. Similar numbers, regional versions and standard versus high-capacity products can cause confusion. A multipack may omit a colour that your printer requires, or include a black cartridge designed for a different purpose from the one you need.

Read the selected listing option carefully. A photo can show a whole colour set while the price applies to a single cartridge. Establish whether you are buying original, third-party compatible or remanufactured supplies, and read the seller's compatibility and support information for that specific product.

Use page yield as a comparison estimate

Published yield figures can help compare standard and high-capacity cartridges when they use a comparable test method. Epson explains that actual output varies with factors including page content, settings, paper and frequency of use. A page count is therefore not a promise that every household will print that many photographs or documents.

For a hypothetical black cartridge, £18 divided by a stated 300-page yield is 6p per test page. A £28 version with a comparable 700-page yield is 4p per test page. Those calculations exclude paper, other ink, maintenance and the printer itself. They are useful for comparing the two stated yields, not for predicting the exact cost of every page.

Colour printing needs particular care because more than one cartridge may be used for a page. Do not divide the price of one colour cartridge by a combined-set figure and describe the result as the complete colour-printing cost. If the manufacturer explains how the figure is calculated, keep that basis with your comparison.

Buy for the printing you expect

A larger cartridge may offer a lower test-page cost but require more money upfront. Consider how frequently you print and whether the printer is likely to remain in use. Buying several spare sets for a machine you may soon replace creates a compatibility risk that the lower unit price does not show.

Check any storage or use-by guidance on the packaging. Keep cartridges sealed until needed, following the manufacturer's directions. If an offer is tied to an ink subscription, compare the subscription terms separately; the monthly charge, page allowance and cancellation conditions are a different purchase model from owning a spare cartridge outright.

Before paying, make one final comparison of model code, colours, quantity, declared yield and delivered cost. Save those details with the order. The next purchase becomes easier when the record says exactly which cartridge worked in your printer, rather than merely remembering that a particular box looked familiar.