中文：

速算扣除数是计算个人所得税时，根据税法规定和计算公式得出的一个固定数值，用于快速计算应纳税额。

根据税法规定，个人所得税的计算公式为：应纳税所得额×适用税率-速算扣除数。其中，应纳税所得额是纳税人取得的收入减去税法规定的各项扣除后的余额；适用税率是根据税法规定和纳税人所得情况确定的税率；速算扣除数是税法规定的用于快速计算应纳税额的固定数值。

速算扣除数的计算方法是根据税法规定和纳税人所得情况而定的。例如，个人所得税中工资、薪金所得适用的速算扣除数为500元，即当应纳税所得额在5000元以下时，可以减去500元的固定数额后再计算应纳税额。

速算扣除数的使用可以大大简化个人所得税的计算过程，特别是对于那些收入较高、所得来源多样化的人来说，能够快速、准确地计算出应纳税额。

英文：

The quick calculation deduction number is a fixed value obtained from the tax law and calculation formula when calculating personal income tax. It is used to quickly calculate the taxable amount.

According to the tax law, the calculation formula for personal income tax is: taxable income × applicable tax rate - quick calculation deduction number. Among them, the taxable income is the net amount of income obtained by the taxpayer after deducting various expenses stipulated by the tax law; the applicable tax rate is the tax rate determined according to the tax law and the taxpayer's income situation; the quick calculation deduction number is a fixed value stipulated by the tax law for quick calculation of the taxable amount.

The calculation method of the quick calculation deduction number is determined according to the tax law and the taxpayer's income situation. For example, the quick calculation deduction number for salaries and wages income in personal income tax is 500 yuan, which means that when the taxable income is less than 5000 yuan, 500 yuan can be subtracted from the fixed amount before calculating the taxable amount.

The use of quick calculation deduction numbers can greatly simplify the calculation process of personal income tax, especially for those with high incomes and diversified sources of income, enabling them to quickly and accurately calculate the taxable amount.