Arithmetic Sequence Calculator
nth term and sum of an arithmetic series.
Enter your values
Enter the first term you are working with.
Enter the common difference you are working with.
Enter the term number you are working with.
Results update instantly as you type — no submit needed. Your values are remembered on this device, and the shareable link reopens the calculator with exactly these numbers.
- Term 20
- 98
- Sum of first n terms
- 1010
- Common difference
- 5
- First terms
- 3, 8, 13, 18, 23, 28, 33, 38, 43, 48
Quick answer
In an arithmetic sequence each term adds a fixed common difference, so the nth term is a₁ + (n−1)d.
aₙ = a₁ + (n−1)d, Sₙ = n/2 (a₁ + aₙ)
At a glance
| What it does | nth term and sum of an arithmetic series. |
|---|---|
| Category | Math |
| Inputs needed | First term, Common difference, Term number |
| Main output | Term 20 |
| Formula | aₙ = a₁ + (n−1)d, Sₙ = n/2 (a₁ + aₙ) |
| Cost | Free — no sign-up, no download |
How to use the Arithmetic Sequence Calculator
- 1Enter the first term of the sequence.
- 2Enter the common difference between terms.
- 3Enter which term number you want.
Inputs explained
- First term
- Enter the first term you are working with.
- Common difference
- Enter the common difference you are working with.
- Term number
- Enter the term number you are working with.
Worked example
Using the values the calculator loads with:
Inputs
- First term3
- Common difference5
- Term number20
Results
- Term 2098
- Sum of first n terms1010
- Common difference5
- First terms3, 8, 13, 18, 23, 28, 33, 38, 43, 48
Frequently asked questions
What if the difference is negative?
The sequence decreases; the formulas still work exactly the same.
How is this different from geometric?
Arithmetic adds a constant, geometric multiplies by a constant.
What do I need to enter into the Arithmetic Sequence Calculator?
Just 3 values: first term, common difference, term number. Every field starts with a realistic example, so you can change one number at a time and watch the result update instantly.
How does the Arithmetic Sequence Calculator work out the answer?
In an arithmetic sequence each term adds a fixed common difference, so the nth term is a₁ + (n−1)d. It applies the formula aₙ = a₁ + (n−1)d, Sₙ = n/2 (a₁ + aₙ) and shows the working so you can check each step by hand.
Is the Arithmetic Sequence Calculator free, and do I need an account?
It is completely free with no sign-up, no download and no usage limit. Everything is calculated in your browser, so the numbers you type never leave your device.
Results are estimates for general information. For medical, legal, structural or financial decisions, confirm with a qualified professional.