The calculation of the basic and diluted earnings per share is based on the following data:

2017
£m
2016
£m
Earnings
Earnings for the purpose of basic earnings per share being net profit attributable to equity holders of the parent97.167.0
NumberNumber
Number of shares
Weighted average number of ordinary shares for the purpose of basic earnings per share190,250,855190,166,794
Effect of dilutive potential ordinary shares:
Share options
Weighted average number of ordinary shares for the purpose of diluted earnings per share190,250,855190,166,794
PencePence
Earnings per share:
Basic51.035.2
Diluted51.035.2
£m£m
Headline earnings
Net profit attributable to equity holders of the parent97.167.0
Add back:
Amortisation of acquired intangible fixed assets (net of tax)2.92.8
Acquisition costs (net of tax)0.5
Less:
Impact of US Tax Cuts and Jobs Act treated as an exceptional item(6.4)
Headline earnings93.670.3
PencePence
Headline earnings per share:
Basic49.237.0
Diluted49.237.0