Mathematics · Precalculus
Arithmetic Series Calculator
Calculate the sum of the first n terms of an arithmetic sequence.
Inputs and results stay in this browser. Change one value at a time to explore the relationship.
Calculation steps
- Last term = 5 + (10−1)×3 = 32.
- Average first and last = (5+32)÷2 = 18.5.
- Sum = 10 × 18.5 = 185.
Problem → model → reason → result
What problem does this model solve?
Calculate the sum of the first n terms of an arithmetic sequence.
Why does the model apply?
Pairing terms from opposite ends gives repeated pairs with the same sum, producing the compact series formula.
What assumptions does it make?
The entered values lie in the function's real domain, the stated sequence or function family matches the problem, and angle units are used consistently.
Formula
Sₙ = n/2[2a₁+(n−1)d]
Calculation and working
The calculator above substitutes your inputs into the model and leaves the calculation steps visible so the answer can be checked rather than merely accepted.
What does the result mean?
The result answers the stated problem in the units implied by your inputs. Read its sign, size and units together, then compare it with the original values before drawing a conclusion.
Worked example
The first 10 terms starting at 5 with difference 3 sum to 185.
Common mistake
A sequence lists terms; a series adds them.
When does this model not apply?
A numerical function value does not by itself establish a trend outside the chosen domain, and finite sequences should not be treated automatically as infinite ones.
How to learn with this calculator
Begin with the worked example, then change one value while keeping the others fixed. Compare the new result and calculation steps to identify which part of the formula changed.
Clear answers
Frequently asked questions
What does the Arithmetic series do?
Calculate the sum of the first n terms of an arithmetic sequence.
How does the Arithmetic series work?
The calculator applies Sₙ = n/2[2a₁+(n−1)d]. Pairing terms from opposite ends gives repeated pairs with the same sum, producing the compact series formula.
What can I learn from the Arithmetic series?
It connects the mathematical rule to your chosen numbers and shows each calculation step. Change one input at a time to see how the result responds.
Does MW SysArc receive or store what I enter?
No. The calculation runs locally in your browser. MW SysArc does not receive or store your calculation inputs.
How should I use the result?
Use the steps to understand the method, then verify important school or professional work using the notation and rounding rules required in your setting.
Last reviewed 2026-07-14. Calculations tested 2026-07-14.