20% of 20 is 4. Twenty percent is one fifth, so 20 ÷ 5 = 4 with no calculator. Decimals agree: 0.2 × 20 = 4. If you already know 20% of 10 is 2, doubling the base doubles the slice—2 × 2 = 4. On this same twenty, 15% of 20 is 3, 25% of 20 is 5, and 30% of 20 is 6, which frames 4 as the clean fifth between a fifteen-percent band and a quarter-plus slice.
Read 20% off £20 as “take away £4,” leaving £16 before postage, VAT, or service charges. If the wording asks only for twenty percent of twenty—commission, tip share, or a budget line—the answer is 4, not sixteen. Swapping “of” for “off” without rereading the prompt is how people quote the wrong side of the twenty-pound line.
Scaling upward keeps the fifth rule intact: 20% of 200 is 40, exactly ten times 4 because the base grew tenfold. Step down to 20% of 25 and you land on 5, still a whole number because twenty-five divides evenly by five. That pattern—fifth-friendly bases versus awkward ones—helps you spot when a mental answer should come out integer versus when decimals are normal.
A base of 20 also pairs neatly with “two tens,” so you can think 20% of one ten is 2 and you have two tens, hence 4. That decomposition matches how people split a twenty-pound note mentally: two tenners, each contributing a two-pound fifth, summed to four pounds off.
If £20 is reduced by 20%, the reduction is £4 and you pay £16 (before other charges).
Change either value below to solve another percentage-of-number question instantly.
Formula used: (percentage ÷ 100) × number
Step 1: Convert 20% → 0.2.
Step 2: Multiply: 0.2 × 20 = 4.
Full formula: (20 ÷ 100) × 20 = 4
Fifth shortcut: 20 ÷ 5 = 4. The percentage figure and the base both being twenty does not change the rule—you still divide the base by five, not “20 by 20.”
Twenty factorises as 2 × 2 × 5. Taking twenty percent removes one factor of five from the “per hundred” story and pairs the remaining twos with the rate’s 0.2, leaving a single 4. When the base is not a multiple of five, the fifth shortcut still works but the result often carries tenths—contrast this page with bases like nineteen, where 20% = 3.8 unless you round for display.
Doubling from ten to twenty is linear: percentage-of scales with the base when the rate is fixed. That is why teaching sequences move from 20% of 10 to this page—the mechanics stay identical while the pounds on the table double.
Fastest: 20 ÷ 5 = 4 (the fifth).
If you know 25% of 20 = 5, shave off 5% of 20 = 1 to reach 4 again—handy when your head anchors on quarters first.
Example 1: Twenty percent off a £20 tee
The markdown is £4 and the ticket price becomes £16 if nothing else stacks on top.
Example 2: Cash-stuffing envelope
Allocating twenty percent of a £20 weekly float to “repairs” sets aside £4, leaving £16 for other envelopes if you follow strict percentages.
Example 3: Small gig fee
A platform quoting 20% of a £20 micro-job payout takes £4; the creator sees £16 before bank fees, not the other way around, unless the contract defines gross differently.
Example 4: Sanity check against two hundred
20% of 200 is 40. Your 4 is exactly one tenth of that slice because 20 is one tenth of 200—a quick order-of-magnitude check when invoices jump a decimal place.
20% of 20 is 4.
Multiply 20 by 0.2, or divide 20 by 5 because 20% is one fifth.
20% off 20 is a reduction of 4, leaving 16.