People work very hard within their normal hours, there are a lot of people who work overtime. This can be to make ends meet, save for a better life, get out debt or save for their first home. The tax on these extra hours make it often pointless to work these hours due to the amount they are taxed.
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If the Government separately taxed overtime hours, at a lower rate, this would enable people to live a better quality of life. Those who are working over their contracted hours would see their hard work paying off.