Inverse Laplace Transform Calculator
Find ℒ⁻¹{F(s)} = f(t) via direct table lookup or partial fraction decomposition — complete step-by-step working for rational functions including exponentials, trig, damped oscillations, and repeated poles.
⚠️ Use * for multiplication, ^ for powers, parentheses for grouping. Handles rational functions with real or complex poles up to degree 4.
Inverse Laplace Transform Result
Click any row to load that F(s) into the calculator instantly.
| F(s) | ℒ⁻¹{F(s)} = f(t) | Notes |
|---|---|---|
| 1/s | 1 | Unit step u(t) |
| k/s | k | Scaled constant |
| 1/s² | t | Ramp function |
| 2/s³ | t² | n!/s^(n+1)→tⁿ |
| 6/s⁴ | t³ | n=3 |
| 24/s⁵ | t⁴ | n=4 |
| F(s) | ℒ⁻¹{F(s)} = f(t) | Notes |
|---|---|---|
| 1/(s−a) | e^(at) | Growing, a>0 |
| 1/(s+a) | e^(−at) | Decaying, a>0 |
| 1/(s+a)² | t·e^(−at) | Repeated root |
| 2/(s−a)³ | t²·e^(at) | 2nd order repeated |
| k/(s−a) | k·e^(at) | Scaled exponential |
| F(s) | ℒ⁻¹{F(s)} = f(t) | Notes |
|---|---|---|
| a/(s²+a²) | sin(at) | Pure sine, a=4 |
| s/(s²+a²) | cos(at) | Pure cosine, a=3 |
| k·s/(s²+a²) | k·cos(at) | Scaled cosine |
| 2/(s²+1) | 2·sin(t) | Scaled sine |
| F(s) | ℒ⁻¹{F(s)} = f(t) | Notes |
|---|---|---|
| a/(s²−a²) | sinh(at) | a=2 |
| s/(s²−a²) | cosh(at) | a=3 |
| 3/(s²−4) | (3/2)·sinh(2t) | Scaled |
| F(s) | ℒ⁻¹{F(s)} = f(t) | Notes |
|---|---|---|
| b/((s+a)²+b²) | e^(−at)·sin(bt) | Damped sine |
| (s+a)/((s+a)²+b²) | e^(−at)·cos(bt) | Damped cosine |
| (s+3)/(s²+2s+5) | e^(−t)[cos(2t)+sin(2t)] | Complete the square |
| (2s+1)/(s²+2s+5) | 2e^(−t)cos(2t)−½e^(−t)sin(2t) | Split numerator |
| 1/((s+2)²+9) | (1/3)e^(−2t)·sin(3t) | 1/b scaling |
| F(s) | ℒ⁻¹{F(s)} = f(t) | Notes |
|---|---|---|
| 1/((s+1)(s+2)) | e^(−t) − e^(−2t) | Distinct real roots |
| s/((s+1)(s+3)) | (3e^(−t)−e^(−3t))/2 | Cover-up method |
| 1/((s+1)(s+2)(s+3)) | ½e^(−t)−e^(−2t)+½e^(−3t) | Three distinct roots |
Complete 40+ pair table with partial fraction rules and ODE examples — all on one printable page.
If F(s) directly matches a standard pair, read f(t) from the table. Always try this first — it's the fastest method.
ℒ⁻¹{1/s}=1 | ℒ⁻¹{1/s²}=t | ℒ⁻¹{a/(s²+a²)}=sin(at) | ℒ⁻¹{s/(s²+a²)}=cos(at)
When the denominator is quadratic with complex roots, complete the square: s²+ps+q → (s+p/2)²+(q−p²/4). Then match to damped sine/cosine pairs.
Example: s²+4s+13 = (s+2)²+9 → a=−2, b=3 → involves e^(−2t)sin(3t) or e^(−2t)cos(3t).
Write F(s) = A/(s−r₁) + B/(s−r₂) + ··· Cover-up for A: multiply by (s−r₁) and set s=r₁.
Example: 1/((s+1)(s+2)) → A=1/(−1+2)=1, B=1/(−2+1)=−1 → e^(−t)−e^(−2t)
Repeated root s=a of order n → n terms: A₁/(s−a)+A₂/(s−a)²+···+Aₙ/(s−a)ⁿ
ℒ⁻¹{1/(s−a)ⁿ} = t^(n−1)·e^(at)/(n−1)!
Complex conjugate pair roots → irreducible quadratic (s+a)²+b². Write (As+B)/((s+a)²+b²), split into damped sin/cos pair. Remember: sine term needs 1/b scaling factor!
(s−a)/((s−a)²+b²) → e^(at)cos(bt) | b/((s−a)²+b²) → e^(at)sin(bt)
If ℒ{f(t)} = F(s), then ℒ⁻¹{F(s−a)} = e^(at)·f(t). Shifting s by a in s-domain multiplies by e^(at) in time domain.
Example: ℒ⁻¹{1/(s−2)²} → substitute a=2 into 1/s² result t → t·e^(2t)
What Is the Inverse Laplace Transform?
This inverse Laplace transform calculator finds ℒ⁻¹{F(s)} = f(t) for any rational function in s — using direct table lookup for standard forms and partial fraction decomposition for more complex expressions. The inverse Laplace transform solver shows complete step-by-step working with the method clearly labeled.
The inverse Laplace transform — written ℒ⁻¹{F(s)} or "L inverse" — reverses the Laplace transform. Given F(s) in the complex frequency domain, the inverse Laplace transform recovers the original time-domain function f(t) such that ℒ{f(t)} = F(s).
The ℒ⁻¹ Symbol Explained
The notation ℒ⁻¹ (also written L⁻¹, "L inverse", or "find l 1") is the inverse Laplace transform operator. It is not a fraction — ℒ⁻¹ means "apply the inverse of the Laplace transform operator ℒ". The result is always a function of time t, valid for t ≥ 0.
Why the Inverse Laplace Transform Matters
- Transform: Take ℒ of the ODE — derivatives become algebraic in s.
- Solve algebraically: Rearrange for Y(s) — pure algebra, no calculus.
- Invert: Apply ℒ⁻¹{Y(s)} = y(t) using the inverse Laplace transform to recover the time-domain solution.
Key insight: The Laplace method converts differential equations (hard) into algebraic equations (easy). The inverse Laplace transform converts the algebraic answer back to the time domain. Table lookup + partial fractions makes ℒ⁻¹ computable without evaluating any integrals.
How to Find the Inverse Laplace Transform — Step-by-Step Method
Use this four-step process to find any inverse Laplace transform reliably. The inverse Laplace transform calculator with steps above automates all four steps.
- Check F(s) is proper: Numerator degree must be less than denominator degree. If not, do polynomial long division first.
- Try direct table lookup: Does F(s) match 1/s, 1/s², a/(s²+a²), s/(s²+a²), 1/(s−a), etc.? If yes, read f(t) directly.
- Partial fraction decomposition: Factor denominator, identify root types (distinct real, repeated, complex conjugate), write partial fraction form, solve for coefficients.
- Sum results: Apply ℒ⁻¹ linearly to each term and sum.
Example 1 — Direct Lookup: ℒ⁻¹{4/(s²+16)}
- Form: a/(s²+a²) → sin(at); a²=16, a=4
- 4/(s²+16) = 1·[4/(s²+16)] → sin(4t)
- f(t) = sin(4t) ✓ Direct table lookup
Example 2 — Repeated Root: ℒ⁻¹{1/(s+1)²}
- Form 1/(s+a)² with a=1 → t·e^(−at)
- Substitute a=1: t·e^(−t)
- f(t) = t·e^(−t) ✓ Direct table (repeated root pair)
Example 3 — Complex Conjugate Roots: ℒ⁻¹{(2s+1)/(s²+2s+5)}
- Complete the square: s²+2s+5 = (s+1)²+4, so a=−1, b=2
- Rewrite numerator: 2s+1 = 2(s+1)−1
- Split: 2(s+1)/((s+1)²+4) − 1/((s+1)²+4)
- Match: 2e^(−t)cos(2t) and (1/2)·[2/((s+1)²+4)] → (1/2)e^(−t)sin(2t)
- f(t) = 2e^(−t)cos(2t) − (1/2)e^(−t)sin(2t)
Inverse Laplace Transform Formula Reference Table
The following table lists all standard inverse Laplace transform pairs. This static HTML table is crawlable and serves as the definitive inverse Laplace transform formula reference.
| F(s) | f(t) = ℒ⁻¹{F(s)} | Condition / Notes |
|---|---|---|
| 1/s | 1 | Unit step u(t) |
| k/s | k | Constant function |
| 1/s² | t | Ramp function |
| n!/s^(n+1) | t^n | n = 1,2,3,... power of t |
| 1/(s−a) | e^(at) | Growing exponential |
| 1/(s+a) | e^(−at) | Decaying exponential |
| 1/(s−a)² | t·e^(at) | Repeated pole at s=a |
| 1/(s−a)^n | t^(n−1)·e^(at)/(n−1)! | nth order pole at s=a |
| a/(s²+a²) | sin(at) | Pure sine oscillation |
| s/(s²+a²) | cos(at) | Pure cosine oscillation |
| a/(s²−a²) | sinh(at) | Hyperbolic sine |
| s/(s²−a²) | cosh(at) | Hyperbolic cosine |
| b/((s−a)²+b²) | e^(at)·sin(bt) | Damped sine |
| (s−a)/((s−a)²+b²) | e^(at)·cos(bt) | Damped cosine |
| s/(s²+a²)² | t·sin(at)/(2a) | Resonance term |
| 1/((s+a)(s+b)) | (e^(−at)−e^(−bt))/(b−a) | Distinct real roots, a≠b |
| s/((s+a)(s+b)) | (b·e^(−bt)−a·e^(−at))/(b−a) | Numerator = s |
| 1/(s+a)² | t·e^(−at) | Repeated pole |
| 2a³/(s²+a²)² | sin(at)−at·cos(at) | Double complex pole |
| 2as/(s²+a²)² | t·sin(at) | Resonance cosine |
Complete 40+ pair table with partial fraction rules — printable PDF.
Partial Fraction Decomposition for Inverse Laplace Transforms
Partial fraction decomposition is the core technique for the inverse Laplace transform of rational functions that don't directly match a table entry. Three root cases apply.
Case 1 — Distinct Real Roots
Example: ℒ⁻¹{1/((s+1)(s+2))}
- Write: A/(s+1) + B/(s+2)
- A = [(s+1)·F(s)] at s=−1 = 1/(−1+2) = 1
- B = [(s+2)·F(s)] at s=−2 = 1/(−2+1) = −1
- ℒ⁻¹{1/(s+1)} − ℒ⁻¹{1/(s+2)} = e^(−t) − e^(−2t)
- f(t) = e^(−t) − e^(−2t)
Case 2 — Repeated Real Roots
Case 3 — Complex Conjugate Roots
Example: ℒ⁻¹{(s+3)/(s²+2s+5)}
- Complete square: s²+2s+5 = (s+1)²+4, α=1, β=2
- Rewrite numerator: s+3 = (s+1)+2
- Split: (s+1)/((s+1)²+4) + 2/((s+1)²+4)
- Match: e^(−t)cos(2t) + e^(−t)sin(2t)
- f(t) = e^(−t)[cos(2t) + sin(2t)]
Common Mistakes When Finding the Inverse Laplace Transform
Mistake 1 — Not Completing the Square
- ❌ Matching (s²+2s+5) directly to (s²+a²) — wrong, the middle term breaks it.
- ✅ Complete the square first: s²+2s+5 = (s+1)²+4, then match to ((s−a)²+b²).
Mistake 2 — Sign Error on the Exponent
- ❌ ℒ⁻¹{1/(s+3)} = e^(3t) — wrong sign.
- ✅ 1/(s+3) = 1/(s−(−3)), so a=−3 → e^(−3t). The pair is 1/(s−a)→e^(at).
Mistake 3 — Forgetting the 1/b Scaling on Sine
- ❌ ℒ⁻¹{1/((s+1)²+4)} = e^(−t)sin(2t)
- ✅ The pair is b/((s−a)²+b²)→e^(at)sin(bt). Here b=2, so factor: (1/2)·[2/((s+1)²+4)] → (1/2)e^(−t)sin(2t)
Mistake 4 — Improper Rational Function
- ❌ Applying table to (s²+1)/s without dividing first.
- ✅ Long divide: (s²+1)/s = s + 1/s → ℒ⁻¹{s}+ℒ⁻¹{1/s} = δ'(t)+1.
Mistake 5 — Confusing sinh/cosh with sin/cos
- ❌ Matching a/(s²−a²) to the sine pair a/(s²+a²).
- ✅ Minus sign in denominator → hyperbolic: a/(s²−a²) → sinh(at), not sin(at).
Worked Examples — Inverse Laplace Transform Problems
1. ℒ⁻¹{6/s³}
- Match n!/s^(n+1) → t^n: n=2 gives 2/s³ → t²
- 6/s³ = 3·(2/s³) → 3t²
- f(t) = 3t²
2. ℒ⁻¹{s/(s²+9)}
- Form s/(s²+a²) → cos(at); a²=9, a=3
- f(t) = cos(3t)
3. ℒ⁻¹{3/(s²−4)}
- Form a/(s²−a²) → sinh(at); a²=4, a=2
- 3/(s²−4) = (3/2)·[2/(s²−4)] → (3/2)sinh(2t)
- f(t) = (3/2)sinh(2t)
4. ℒ⁻¹{(3s+5)/(s²+4s+13)}
- Complete square: s²+4s+13=(s+2)²+9, α=2, β=3
- Numerator: 3s+5=3(s+2)+(5−6)=3(s+2)−1
- Split: 3(s+2)/((s+2)²+9) − 1/((s+2)²+9)
- 3e^(−2t)cos(3t) − (1/3)e^(−2t)sin(3t)
- f(t) = e^(−2t)[3cos(3t) − (1/3)sin(3t)]
5. ℒ⁻¹{1/((s+1)(s+2)(s+3))}
- Partial fractions: A/(s+1)+B/(s+2)+C/(s+3)
- A=[1/((s+2)(s+3))] at s=−1 = 1/(1·2)=1/2
- B=[1/((s+1)(s+3))] at s=−2 = 1/(−1·1)=−1
- C=[1/((s+1)(s+2))] at s=−3 = 1/(−2·−1)=1/2
- f(t) = (1/2)e^(−t) − e^(−2t) + (1/2)e^(−3t)
6. ℒ⁻¹{(2s²+5)/(s(s²+4))}
- Partial fractions: A/s+(Bs+D)/(s²+4)
- A=[s·F(s)] at s=0 = 5/4
- Equate s² coeff: A+B=2 → B=3/4; s¹: D=0
- ℒ⁻¹{(5/4)/s}+ℒ⁻¹{(3/4)s/(s²+4)} = 5/4+(3/4)cos(2t)
- f(t) = 5/4+(3/4)cos(2t)
7. ODE Example: y''+4y=0, y(0)=1, y'(0)=0
- Laplace transform: (s²+4)Y(s)−s=0
- Y(s)=s/(s²+4)
- ℒ⁻¹{s/(s²+4)}=cos(2t)
- y(t)=cos(2t) ✓
8. ℒ⁻¹{(s+1)/(s²(s+2))}
- Partial fractions: A/s+B/s²+C/(s+2)
- B=[s²·F(s)] at s=0=1/2; C=[(s+2)·F(s)] at s=−2=(−1)/4=−1/4
- A+C=0 (s² coeff) → A=1/4
- f(t)=1/4+(1/2)t−(1/4)e^(−2t)
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Full reference table, partial fraction rules, and ODE guide — free printable PDF.
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