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Bid-Ask Calculator

Calculate bid-ask spread. Free online Bid-Ask Calculator. Calculate bid-ask online — fast, accurate, mobile-friendly, no signup needed.

Spread
$0.50
Spread %
0.5%

Derivation

  1. ├── 01Givenbid = 99.5, ask = 100
  2. ├── 02FormulaSpread: e.ask-t
  3. ├── 03Substitutee.100-t
  4. ├── 04Compute Spread$0.50
  5. ├── 05FormulaSpread %: {let t=e.bid,a=e.ask;return(a-t) / a × 100}
  6. ├── 06Substitute{let t=e.99.5,a=e.100;return(a-t) / a × 100}
  7. └── 07Compute Spread %0.5
Did you know?

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§01What is

Understanding the Bid-Ask Calculator

The Bid-Ask Calculator computes Spread from 2 inputs: bid ($), ask ($). Calculate bid-ask spread.

Quick calculators for the math that shouldn’t need a notepad — instant, accurate, private to your browser. The Bid-Ask Calculator sits in that toolkit — it calculate bid-ask spread. Enter your numbers above and the result updates instantly; every step of the math is shown in the Derivation panel so you can see exactly how the answer was reached.

§02The Formula

How it’s calculated

Spread = e.ask-t | Spread % = {let t=e.bid,a=e.ask;return(a-t) / a × 100}

Where

bid
Bid ($)
ask
Ask ($)
Spread
Output value
Spread %
Output value
§03Practical Example

Step-by-step walkthrough

Scenario

Apply the formula to a realistic set of inputs: Bid ($) = 99.5, Ask ($) = 100.

  1. 01Start by noting the input — Bid ($): 99.5.
  2. 02Start by noting the input — Ask ($): 100.
  3. 03Substitute these values into the formula: Spread = e.ask-t | Spread % = {let t=e.bid,a=e.ask;return(a-t) / a × 100}
  4. 04Compute Spread: the calculator returns 0.5.
  5. 05Compute Spread %: the calculator returns 0.5.
  6. 06Cross-check the answer by opening the Derivation panel above — every line of math is shown so you can follow the computation end-to-end.
§04Variants

Common Bid-Ask Problems

The formula gets rearranged depending on which variable you need. Here are the patterns you’ll run into in the real world — find the one that matches your problem and follow the worked steps.

01 · PATTERN

Bid ($) halved

bid = 49.75 (from 99.5)

Keep every other input at its default and halve the bid ($). See how spread responds.

  1. 01New Bid ($): 49.75
  2. 02Baseline Spread: 0.5
  3. 03New Spread: 50.25
  4. 04Spread increases by 9950% → use this sensitivity to plan for real-world variation.
02 · PATTERN

Bid ($) doubled

bid = 199 (from 99.5)

Keep every other input at its default and double the bid ($). See how spread responds.

  1. 01New Bid ($): 199
  2. 02Baseline Spread: 0.5
  3. 03New Spread: -99
  4. 04Spread decreases by 19900% → use this sensitivity to plan for real-world variation.
03 · PATTERN

Ask ($) halved

ask = 50 (from 100)

Keep every other input at its default and halve the ask ($). See how spread responds.

  1. 01New Ask ($): 50
  2. 02Baseline Spread: 0.5
  3. 03New Spread: -49.5
  4. 04Spread decreases by 10000% → use this sensitivity to plan for real-world variation.
04 · PATTERN

Ask ($) doubled

ask = 200 (from 100)

Keep every other input at its default and double the ask ($). See how spread responds.

  1. 01New Ask ($): 200
  2. 02Baseline Spread: 0.5
  3. 03New Spread: 100.5
  4. 04Spread increases by 20000% → use this sensitivity to plan for real-world variation.
§05FAQ

Frequently asked questions

Yes. The calculator implements the standard formula as documented and returns exact floating-point results. No approximations are used unless noted in the formula.
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