Interest is charged at a flat rate of 11%.

利息按标准比率11%收取。

《牛津词典》

Fees are charged at a flat rate, rather than on a percentage basis.

费用按固定的费率收取，不是按百分比。

《柯林斯英汉双解大词典》

We pay a flat rate for every telephone call.

我们打电话每次付相同的费用。

youdao

The personal income tax is not simple; it's not just a flat rate on your income, it depends on the type of income.

个人所得税计税方法并不简单,并不是统一的征收税率,而是取决于你收入的类型

耶鲁公开课 - 金融市场课程节选

Likewise, in Indiana, the economy boomed after a flat rate went into effect in 2003.

FORBES: Death Is Much Less Complicated Than The U.S. Tax Code

The strikers want this system extended to cable TV ads, which currently pay a flat rate.

BBC: Strikers attract star support

Taxes are levied at a flat rate on all distillers, irrespective of their size.

ECONOMIST: Start-ups are shaking up an old and staid industry