How to Calculate Percentage: Formulas, Examples & Excel

The core percentage formula divides the part by the whole, then multiplies by 100. This guide walks you through that formula, real-world examples like 20% of 70, and how to automate percentage calculations in Excel, step by step.

Basic Formula: (part ÷ whole) × 100 ·
20% of 70: 14 ·
5% of 300: 15 ·
30% of 300: 90 ·
2% of 5: 0.1

How do I calculate percentage of a number?

The core percentage formula divides the part by the whole, then multiplies by 100. Microsoft Support provides the standard: (part ÷ whole) × 100. This applies whether you’re calculating a test score, a share of sales, or any proportional relationship.

Basic formula steps

• Identify the part — the specific amount you want to express as a percentage (e.g., 14).
• Identify the whole — the total or reference amount (e.g., 70).
• Divide part by whole — 14 ÷ 70 = 0.2.
• Multiply by 100 — 0.2 × 100 = 20%.

Excel translates this directly: enter =A1/B1*100 in a cell, where A1 is the part and B1 is the whole (Academy of Learning). Format the result cell as a percentage using Ctrl+Shift+% on Windows to display it correctly.

Examples like 20% of 70

• 20% of 70: 70 × 0.20 = 14. The reverse check: 14 ÷ 70 × 100 = 20%.
• 5% of 300: 300 × 0.05 = 15.
• 30% of 300: 300 × 0.30 = 90.
• 2% of 5: 5 × 0.02 = 0.1.

The 1% trick simplifies mental math: find 1% by dividing by 100, then scale up. For 30% of 300, first calculate 1% (3), then multiply by 30 to get 90 (Excel Easy).

How do I take 20% off a price?

Discounting a price requires multiplying by a number less than 1 — specifically (1 − discount). Excel Easy explains the approach: original price × (1 − discount percentage). If something costs $70 and you want 20% off, the calculation is 70 × (1 − 0.20) = $56.

Discount calculation method

• Convert percentage to decimal: 20% = 0.20.
• Subtract from 1: 1 − 0.20 = 0.80.
• Multiply original price: 70 × 0.80 = $56.

To find what percentage was actually discounted, use the reverse: (original − sale) ÷ original × 100. A price dropping from $70 to $59.50 gives (70 − 59.50) ÷ 70 = 0.15, or 15% off (Exceljet). Shoppers can check whether they are truly getting the advertised discount by applying this calculation.

Step-by-step price reduction in Excel

For spreadsheet automation, Dummies recommends the formula =A2-(A2*B2), where A2 holds the original price and B2 holds the discount rate as a decimal (Dummies). This gives you the final price directly. Format B2 as a percentage, and Excel handles the display correctly.

Want to reverse-engineer the original price from a sale price? Microsoft Support provides the formula: original = sale ÷ (1 − discount). If you paid $15 for an item advertised as 25% off, the original price was 15 ÷ 0.75 = $20 (Microsoft Support). This helps budget-conscious shoppers verify whether a deal truly delivers the savings claimed.

What is the easiest way to calculate percentage?

The fastest mental route starts with 1%. Divide the number by 100, then multiply by the desired percentage. This works for any whole number and avoids reaching for a calculator in everyday situations like tipping or quick estimates at checkout.

Mental math shortcuts

• Find 1% first: 70 ÷ 100 = 0.70.
• Scale to your target: For 20%, multiply 0.70 × 20 = 14.
• Use 10% benchmarks: 10% of 70 is 7; double it for 20% to get 14.

Corporate Finance Institute notes that the percentage change formula — (new ÷ old) − 1 — also works for quick comparisons between two values (Corporate Finance Institute). This is especially useful when comparing prices or scores over time without needing the full percentage-of-whole calculation. Quick estimators who master the 10% benchmark can scale to any percentage without reaching for their phone.

1% then scale up

For 30% of 300: find 1% (3), then multiply by 30 to get 90. For 5% of 70: find 1% (0.70), multiply by 5 to get 3.5. This method generalizes to any percentage without requiring the full formula each time.

In Excel, the same principle applies when building formulas: =A1*0.30 calculates 30% directly. For reusable templates, set up a column for the percentage (formatted as %) and reference it with =A1*B1, where B1 holds your percentage value.

How to calculate percentage in Excel?

Excel’s percentage formulas follow the same core logic as manual calculation, with formatting handling the display. The key is understanding the two steps: the arithmetic (dividing and multiplying) and the cell formatting (Ctrl+Shift+% or Home → Number → Percentage).

Formula syntax

• Percentage of a number: =(A1/B1)*100 or simply =A1/B1 with percentage formatting applied.
• Discounted price: =A2-(A2*B2) where A2 is original price and B2 is discount rate as decimal (BeProfit).
• Percentage increase: =A1*(1+B1) where B1 is the increase rate (e.g., 0.10 for 10%).

Microsoft Support provides the official reference: to apply a percentage increase like 6.75%, enter the formula =(2500-2342)/2342 with the result formatted as percentage (Microsoft Support). The cell will display 6.75% after formatting. Spreadsheet builders who remember to format first avoid the common trap of seeing decimals instead of percentages.

Common functions

• Percentage of total: =A1/B$1 — fix the denominator row with $ to drag the formula down across multiple items.
• Percent change between two values: =(new-old)/old formatted as percentage — positive result means increase, negative means decrease (Academy of Learning).
• Goal Seek for reverse calculations: Use Data → What-If Analysis → Goal Seek to set a target price and have Excel solve for the required discount rate (BeProfit).

Common error to avoid: forgetting to format as percentage shows decimals like 0.15 instead of 15%. Always apply percentage formatting (Ctrl+Shift+%) after entering a percentage calculation formula (YouTube Percentage Formula Tutorial).

How to calculate percentage increase?

A percentage increase measures how much a value has grown relative to its starting point. Microsoft Support defines the formula as (new − old) ÷ old, then format the result as a percentage (Microsoft Support). The same formula applies whether you’re tracking sales growth, price changes, or student marks over time.

Change over time

• Identify old value (starting point).
• Identify new value (ending point).
• Apply formula: (new − old) ÷ old × 100 (or ÷ old with percentage formatting).

Excel Easy gives the example of a value growing from 2342 to 2500: (2500 − 2342) ÷ 2342 ≈ 0.0675, which formats as 6.75% increase. For a decrease, the same formula produces a negative result — (2425 − 2500) ÷ 2500 = −0.03, or −3% (Microsoft Support). Investors who monitor percentage changes spot trends before they become obvious from raw numbers alone.

Final vs initial

Corporate Finance Institute notes that an alternative formulation — (new ÷ old) − 1 — produces the same result as (new − old) ÷ old (Corporate Finance Institute). Both approaches are mathematically equivalent; choose based on readability. For marks improvement: if a student scored 70 previously and now scores 85, the improvement is (85 − 70) ÷ 70 ≈ 21.4%.

When applying an increase to a value (rather than measuring it), Dummies explains to multiply by 1 + percentage: to increase $100 by 10%, calculate 100 × 1.10 = $110. To decrease, multiply by (1 − percentage): 1000 × 0.80 = $800 for a 20% discount (Dummies). Retailers who apply the correct multiplier avoid undercharging or overcharging customers.

How to calculate percentage of marks?

Calculating percentage of marks follows the identical formula as any other percentage calculation: (marks obtained ÷ total marks) × 100. The process doesn’t change whether you’re tracking six subjects or a single test — you divide the part by the whole.

Multi-subject calculation

• Step 1: Sum marks obtained across all subjects (e.g., 450 out of 600 total).
• Step 2: Divide by total: 450 ÷ 600 = 0.75.
• Step 3: Multiply by 100: 0.75 × 100 = 75%.

In Excel, set up columns for each subject’s marks and total, then use =SUM(B2:F2)/SUM($B$1:$F$1)*100 to get a total percentage across six subjects. Academy of Learning notes that the same percentage change formula applies when comparing marks over time: (new marks − old marks) ÷ old marks (Academy of Learning).

Weighted averages

If subjects carry different weights (e.g., science counts 40%, humanities 60%), calculate weighted contribution: (subject_score × weight) ÷ total_weight × 100, then sum each subject’s weighted contribution. Excel handles this with =SUMPRODUCT or a manual formula summing each (score × weight) pair divided by total weight.

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The percentage formulas discussed here align with those in the percentage formulas guide, offering extra examples for discounts and increases in Excel.

Frequently asked questions