One weight per value. Weights can be decimals (0.5) or counts (5) — they are normalized automatically.
Calculation details
Planning estimate only, not financial, tax, or legal advice. Verify assumptions and current rules before making decisions.
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Use this result
Share the current inputs or ask ChatGPT to explain the calculation in context.
What does this calculator estimate?
A student scoring 90 on a quiz worth 20 percent and 75 on a final worth 80 percent has a weighted average of (90 x 20 + 75 x 80) / 100 = 78. The weights must sum to 100 percent for this form.
- Weighted average = sum of (value x weight) divided by sum of weights.
- Weights can be any non-negative numbers, not just percentages (NIST).
- A simple average weights every value equally; a weighted average does not.
When to use a weighted average
A plain average treats every value equally; a weighted average gives each value its proper influence — course credits for grades, portfolio weights for returns, units for prices. It's the correct average whenever items have different importance.
Limitations to watch for
Weights must match values in order and count. The scale of weights doesn't matter (all weights ×10 changes nothing), but zero or negative weights behave differently — use positive weights. Percent weights should sum to 100%.
How to use it in practice
List each value with its weight (credits, shares, category importance). Use it for GPA-style calculations, weighted portfolio returns, and survey scores. Check the plain mean too — the gap shows how much the weighting changes the result.
['Enter the values.', 'Enter the matching weights.', 'Read the weighted average.']
What a weighted average is
A weighted average multiplies each value by its weight before averaging: grades worth 20 and 80 percent, or portfolio holdings by share. The formula is Σ(value × weight) ÷ Σ(weight). The calculator applies it to any set.
When to use it
Weighted averages are correct when items contribute unequally: course grades by credit weight, portfolio returns by allocation, survey results by group size. A plain average misstates all of these — the calculator prevents the error.
Weights must sum sensibly
Weights can be percentages that sum to 100 or arbitrary units that sum to anything — the formula normalizes either way. The calculator accepts both, so course weights (0.2, 0.8) and share counts (10, 5 shares) both work.
A worked example
Grades of 90 (20% weight) and 70 (80%): weighted average = 90×0.2 + 70×0.8 = 18 + 56 = 74 — versus a plain average of 80. The calculator makes the weight's influence explicit.
Weighted vs. arithmetic in data
Financial returns and repeated measures often need weighting by capital or time. Using an unweighted average overstates small positions. The calculator is the correct tool whenever items differ in importance.
How this calculator works
Formula
Weighted average = Σ(value × weight) ÷ Σ(weights). Weights need not sum to 1 — any positive numbers work.
Worked example
A 90 on a 2-credit course and a 70 on a 1-credit course: (90×2 + 70×1) ÷ 3 = 83.33.
Assumptions to verify
- Values and weights align by position.
- Weights are non-negative.
- The weighting reflects the intended importance.
Frequently asked questions
What is a weighted average?
An average where each value is multiplied by its weight: Σ(v×w) ÷ Σw. (90×2 + 70×1) ÷ 3 = 83.33.
When should I use it?
When items have different importance — course credits, portfolio holdings, or survey categories.
Do weights have to add to 100%?
No — any positive weights work; the formula normalizes automatically.
What's the difference from a plain average?
A plain average treats all values equally; a weighted average gives influence proportional to the weights.
How is GPA a weighted average?
Each grade's points are weighted by course credits: a 4-credit A outweighs a 2-credit B.
What if I use percentages as weights?
That works — percentage weights sum to 100 and produce the same result.
What does a big gap between mean and weighted mean tell me?
High-weight items are pulling the result — important when those items matter most.
Do weights need to sum to 100?
No — the formula normalizes any weights.
What is the difference from a plain average?
A plain average treats all items equally; a weighted average respects their importance.
Cite this tool
BoringToolsKit. “Weighted Average Calculator.” boringtoolskit.com/weighted-average-calculator/ (reviewed 2026-08-25). Free to reference in articles, syllabi, and answer posts with a link.
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