Series Convergence Calculator

Enter a series summand (the general term), choose your series type (geometric, p-series, or alternating), and set your start index to test whether your infinite series converges or diverges. For geometric series you get the exact sum; for p-series and alternating series you get the convergence verdict plus the key parameter values that determine it.

Choose the type of infinite series you want to test.

The first term of your geometric series (a). Used for geometric series only.

The common ratio r for geometric series. Converges when |r| < 1.

The exponent p for p-series or alternating series. P-series converges when p > 1.

The index at which the series summation begins (usually 0 or 1).

Number of terms to compute for the partial sum approximation.

Results

Convergence Result

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Exact Sum (S)

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Partial Sum (N terms)

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Key Parameter Value

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Convergence Margin

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Partial Sum Growth (First N Terms)

Results Table

Frequently Asked Questions

What is series convergence and why does it matter?

A series converges when the infinite sum of its terms approaches a finite, definite value. If the sum grows without bound or oscillates indefinitely, the series diverges. Convergence is foundational in calculus, physics, and engineering — it underpins Taylor series, Fourier analysis, and numerical approximation methods.

What are the most common tests for series convergence?

The most widely used tests include the Ratio Test (comparing consecutive terms), the Root Test, the Integral Test (relating the series to an improper integral), the Comparison Test (bounding the series against a known one), and the Alternating Series Test. This calculator applies the relevant test automatically based on the series type you select.

When does a geometric series converge?

A geometric series Σ a·rⁿ converges if and only if the absolute value of the common ratio satisfies |r| < 1. When it converges, the exact sum is S = a / (1 − r). If |r| ≥ 1, the terms do not shrink fast enough and the series diverges.

What is a p-series and when does it converge?

A p-series has the form Σ 1/nᵖ, where p is a positive constant. It converges when p > 1 and diverges when p ≤ 1. The classic example is the harmonic series (p = 1), which famously diverges despite its terms approaching zero.

What is the difference between absolute and conditional convergence?

A series is absolutely convergent if the sum of the absolute values of its terms converges. It is conditionally convergent if the series itself converges but the absolute-value series diverges. The alternating harmonic series Σ (−1)ⁿ/n is a well-known example of conditional convergence.

How can I determine if a series is convergent or divergent step by step?

First check whether the terms approach zero (if not, the series definitely diverges). Then identify the series type — geometric, p-series, alternating, etc. — and apply the appropriate convergence test. Compute the key parameter (ratio, p-value, or limit) and compare it against the threshold that determines convergence.

How does series convergence relate to calculus and real-world applications?

Series convergence is central to representing functions as infinite sums via Taylor and Maclaurin series, solving differential equations, and computing integrals that have no closed form. In engineering and physics, Fourier series decompose signals into frequency components, and convergence guarantees those representations are valid and stable.

What is the partial sum and how close is it to the true sum?

The partial sum Sₙ is the sum of the first N terms of the series. For a convergent series, Sₙ approaches the exact infinite sum as N increases. The difference between Sₙ and the true sum is the remainder or error; for alternating series, the error is bounded by the absolute value of the next term in the sequence.

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