Percentage calculator

Fast percentage checks for prices, discounts, mark-ups and everyday comparisons.

Before you calculate

How this percentage calculator estimate fits into a wider plan

The number should be treated as a planning checkpoint rather than an isolated answer. It is most useful when compared with a second scenario, because the difference between two choices often gives a clearer signal than a single calculation.

Keep the inputs consistent when comparing scenarios. Change one assumption at a time, then review how much the result moves. That makes it easier to see whether the decision is being driven by rate, term, contribution, balance, price or another variable.

If the estimate will affect borrowing, tax, savings or repayment decisions, leave a margin of safety. Real budgets include timing issues, irregular bills and changes in income, so the strongest plan is usually the one that still works when the figures are slightly less favourable.

Use percentages to compare changes clearly

Percentages are useful when the size of the change matters more than the raw number. A £20 discount is not the same decision on a £50 item as it is on a £500 item, and a 10% rise can feel different depending on the starting amount.

For money decisions, choose the calculation that matches the question. Use percentage change to compare old and new prices, reverse percentage to find the original price before a discount, and “A% of B” for tax, tips, fees or sale reductions.

Use the result to check the size of the change before acting. For the calculation basis, see the MyFinanceTools methodology.

Quick calculations

Enter the figures you know and the result updates straight away. Useful for quick money maths without hunting for the right formula.

A% of B

Result
—
As fraction
—

What % of B is A?

Percent
—
Ratio A/B
—

Increase B by A%

New value
—
Increase amount
—

Decrease B by A%

New value
—
Decrease amount
—

Percentage change (A → B)

Change
—
Delta
—

Reverse percentage

If B is the final value after a % increase/decrease, find the original.

Original
—
Multiplier
—

After you calculate

Turn the percentage answer into a clear money comparison

A percentage only makes sense when the base number is clear. Ten percent of £50 and ten percent of £5,000 are very different decisions, even though the percentage is identical. Read the result alongside the original amount before using it for a price, bill, salary, debt or savings target.

For discounts and price rises, translate the percentage into pounds. A percentage can make a change sound smaller than it feels in a budget. If a bill rises by 12%, the cash increase is what affects the monthly plan.

For progress checks, state the result in plain language. Instead of only noting “40%”, write what that means: 40% of the target saved, 60% left to go, and the cash amount still needed. That prevents the result being reused without the context that made it accurate.

Percentage checks that prevent misleading comparisons

Do not compare two percentages unless they measure the same thing. APR, tax rate, discount rate, profit margin, pay rise and savings growth all use percentages, but they do not answer the same question.

When the base changes, calculate again. A percentage based on last year’s rent, salary, debt balance or selling price may not explain the current position. For important money decisions, keep the inputs with the answer so it can be checked later.

If the result affects borrowing, tax, pricing or repayment planning, use the percentage as a starting point and then review the cash impact. The percentage shows the relationship; the pound figure shows the practical pressure.