A sum calculator adds up a list of numbers in one step. Paste numbers separated by commas, spaces or line breaks, and it returns the total, often with the count, average, minimum and maximum. Advanced versions also evaluate summation notation (Σ) and the sums of arithmetic and geometric series.
For a simple list, the sum is just everything added together: 12 + 7 + 23 + 9 = 51. Summation notation is a compact way to write long sums. For example, Σ from i = 1 to 5 of i² means 1 + 4 + 9 + 16 + 25 = 55. There are shortcut formulas, too: the sum of the first n whole numbers is n(n + 1) ÷ 2, so 1 + 2 + … + 100 = 5,050, the famous trick attributed to a young Carl Friedrich Gauss.
For an arithmetic series (constant difference), sum = n × (first + last) ÷ 2. The series 3 + 7 + 11 + … + 39 has 10 terms, so the sum is 10 × 42 ÷ 2 = 210. For a geometric series (constant ratio r), sum = a(1 − rⁿ) ÷ (1 − r). For 2 + 6 + 18 + 54, that’s 2(1 − 81) ÷ (1 − 3) = 80.
Everyday uses: totaling receipts, adding up game scores, checking spreadsheet totals and summing hours on a timesheet. Common mistakes include missing a number when copying a list and mixing negative signs. Double-check by estimating or adding in a different order.
Tips for getting accurate results from the Sum Calculator: double-check that every input uses the right units, enter numbers without commas or symbols, and run the calculation a second time with a quick estimate in your head to confirm the answer looks reasonable.
Learn more on Wikipedia’s summation article. Find average, mean absolute deviation and long division calculators on Minedit.