百分比计算器
计算某数的百分比、反推百分比或衡量百分比变化。适用于消费税、折扣和加价。
结果
关于这个百分比计算器
Percentages show up on every Singapore receipt: GST at 9%, a 20% sale, a 10% service charge, a markup from cost to shelf price. This page does three jobs at once. Percent of a number answers “what is 9% of 100?” (9). Is what percent answers “9 is what percent of 100?” (9%). Percent change answers “from 100 to 9, what is the change?” (−91%).
GST is the usual reason to open a percentage tool here. A $100 net bill with 9% GST is $9 tax and $109 total. A $109 GST-inclusive price is not 9% of 109; the net is 109 / 1.09. This calculator’s first card is the forward 9% of a net figure. For GST-inclusive extraction, use the GST calculator on this site.
Discounts compound in the wrong direction if you add percentages naively. 20% off then another 10% off is not 30% off. Compute the first sale price, then take 10% of the new number. Percent change from old to new is (new − old) / |old|.
All three results update as you type. Defaults show 9% of 100 = 9, which matches Singapore GST on a round hundred.
No accounts, no upload. Confirm rounding against your till if a cent matters.
如何使用
- Enter the percent and the base number for “X% of Y”.
- Enter the part to see what percent it is of the base, and the percent change from base to part.
- Read all three result cards.
关键术语与概念
Percent of is (percent / 100) × number.
Is what percent is (part / number) × 100.
Percent change is (part − number) / |number| × 100.
GST 9% is a forward percentage on a GST-exclusive net.
常见用途
- Adding 9% GST to a net quote.
- Checking a 25% staff discount on a $80 item.
- Measuring a pay rise from $4,000 to $4,200 (5%).
- Seeing a price drop from $100 to $9 as −91% (the default third card).
示例
Example 1 — 9% of 100. 9. Singapore GST on $100 net.
Example 2 — 9 is what % of 100. 9%.
Example 3 — change 100 → 9. −91%.
Example 4 — 20% of 80. 16.
重要说明
Divide-by-zero. If the base number is 0, percent-of-part and change return 0 on this page.
GST-inclusive extraction is not this formula — use the GST calculator.
Rounding is to four decimal places in the engine, then displayed as typed.
常见问题
What is 9% of 100?
9. That is GST on a $100 net amount.
How do I calculate a percentage of a number?
Multiply the number by percent/100.
How do I reverse a percentage?
Divide the part by the whole and multiply by 100.
What is percent change?
(new − old) / |old| × 100. From 100 to 9 that is −91%.
Is GST 9% of the inclusive price?
No. 9% applies to the exclusive net. Inclusive tax is amount − amount/1.09.
Can I compute a markup?
Yes. If cost is the base and shelf price is the part, percent change is the markup.
Does this handle negative numbers?
The formulas use the values you type. Percent change uses absolute value in the denominator.
Why three answers at once?
The same three numbers usually answer the receipt, the reverse check, and the change.
Is this Singapore-specific?
The math is universal. Defaults use 9 because that is Singapore GST.
Are numbers stored?
No.