Dyscalculia

Dyscalculia is a specific learning difficulty affecting understanding of numbers, quantity, time, and arithmetic. As the British Dyslexia Association describes it, it's lifelong and distinct from dyslexia, though the two sometimes co-occur. It shows up on the web wherever numerical reasoning is involved: pricing, checkout calculations, time and date entry, charts, and any form asking for amounts or quantities.

The W3C's Cognitive and learning abilities and barriers guidance covers number processing as part of cognitive accessibility. Common barriers include unit conversions left to the user, prices shown without breakdowns, ambiguous free-text date fields, charts that rely on size without numeric labels, and forms that won't accept varied input formats.

Spell out calculations rather than expecting mental arithmetic. Label charts with the actual numbers. Use date and time pickers rather than free-text fields. Accept multiple formats for numbers. Show running totals at checkout.