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Retail Discount and Multi-Buy Comparisons

Calculate percentage or fixed discounts, successive reductions, cheapest-item deals and fixed-price bundles.

  • Formula & worked example
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Calculator inputs

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How to use this calculator

  1. Enter the known values in the units shown. Results update as you type.
  2. Where results are editable, change one to solve backwards. Lock a value to hold it fixed.
  3. Use the worked example to check the method. Reset restores the starting fields.

Use the result with context

Results are estimates for planning and education. Confirm rates, taxes, fees, and legal requirements with the relevant institution or a qualified professional before making a financial decision.

Formula and method

A 100 price reduced by 20%, with tax already included, costs 80 and saves 20.

Successive discounts multiply remaining-price factors. Multi-buy discounts apply to the cheapest included item; apply an entered sales-tax multiplier only when tax is excluded.

Worked example

Enter these known values and leave the other values blank.

Original price
100 USD
Discount
20 %
You pay...
80 USD
You're saving...
20 USD

Assumptions and limitations

  • Use prices on one consistent tax basis. Savings and discounted price use the same tax multiplier; a redundant source identity is corrected so added tax cannot contradict the result.
  • A multi-buy saving is useful only if all included items are needed. Shipping is outside this model.
  • Use one currency throughout. Retained currency selector factors are a historical snapshot, not live exchange rates.
  • Clear an editable unknown before solving an inverse. Selection controls and forced outputs cannot be inferred.

Common questions

What does this model assume?

Use prices on one consistent tax basis. Savings and discounted price use the same tax multiplier; a redundant source identity is corrected so added tax cannot contradict the result.

Can I use the currency menu as a current quote?

No. Keep amounts in one currency; conversion factors are a captured historical snapshot.

References

The calculation follows this reviewed mathematical model: Successive discounts multiply remaining-price factors. Multi-buy discounts apply to the cheapest included item; apply an entered sales-tax multiplier only when tax is excluded. Required model inputs: Discount must be between zero and 100 percent. Bundle count must be a positive whole number.

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