Can't understand a P800

My wife got a P800 and I don't understand this column of figures: Your total taxable income £37497.54 Income Tax rates(s) Personal Savings Allowance at 0% on £1000.00 Basic rate at 20% on £37096.00 Total £38096.00 I don't see where 37096.00 comes from; what am I missing? There is nothing complicated about her tax affairs; she is a pensioner paying tax on a building society interest for the first time in years.

Hi,
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