About the Arithmetic Series Calculator
Sum an arithmetic series from its first and last terms or first term and common difference, with the number of terms.
Also known as: sum of arithmetic series, arithmetic sum, sum of ap.
How to use this calculator
- Enter first term, last term, common difference.
- The result updates instantly as you type — press Calculate (or Enter) at any time.
- Open “Step-by-step” to see how the answer was worked out.
- Use Copy result or Share to save the answer or send a link with your inputs.
Formula
S = n(a₁ + aₙ)/2, n = (aₙ − a₁)/d + 1
Worked example
Using the values pre-filled in the calculator above:
- First term = 5
- Last term = 95
- Common difference = 5
the calculator returns:
- Sum: 950
- Number of terms: 19
Working
n = (95 − 5) ÷ 5 + 1 = 19S = 19/2 × (5 + 95) = 950