Extrapolation Calculator
Linear extrapolation beyond two known points.
Enter your values
Enter the x₁ you are working with.
Enter the y₁ you are working with.
Enter the x₂ you are working with.
Enter the y₂ you are working with.
Enter the target x 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.
- Extrapolated y
- 21
- Slope
- 2
- Equation
- y = 2x + 1
- Type
- Extrapolation (outside the data)
Quick answer
Linear extrapolation extends the straight line through two known points: y = y₁ + (x − x₁) × (y₂ − y₁) ÷ (x₂ − x₁).
y = y₁ + (x − x₁)(y₂ − y₁)/(x₂ − x₁)
At a glance
| What it does | Linear extrapolation beyond two known points. |
|---|---|
| Category | Math |
| Inputs needed | x₁, y₁, x₂, y₂, Target x |
| Main output | Extrapolated y |
| Formula | y = y₁ + (x − x₁)(y₂ − y₁)/(x₂ − x₁) |
| Cost | Free — no sign-up, no download |
How to use the Extrapolation Calculator
- 1Enter the first known point.
- 2Enter the second known point.
- 3Enter the x you want to project to.
Inputs explained
- x₁
- Enter the x₁ you are working with.
- y₁
- Enter the y₁ you are working with.
- x₂
- Enter the x₂ you are working with.
- y₂
- Enter the y₂ you are working with.
- Target x
- Enter the target x you are working with.
Worked example
Using the values the calculator loads with:
Inputs
- x₁1
- y₁3
- x₂4
- y₂9
- Target x10
Results
- Extrapolated y21
- Slope2
- Equationy = 2x + 1
- TypeExtrapolation (outside the data)
Frequently asked questions
Is extrapolation reliable?
Only near the data range — the further you go beyond it, the more the straight-line assumption can break down.
What's the difference from interpolation?
Interpolation estimates inside the known range; extrapolation projects outside it.
What do I need to enter into the Extrapolation Calculator?
Just 5 values: x₁, y₁, x₂, y₂, target x. 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 Extrapolation Calculator work out the answer?
Linear extrapolation extends the straight line through two known points: y = y₁ + (x − x₁) × (y₂ − y₁) ÷ (x₂ − x₁). It applies the formula y = y₁ + (x − x₁)(y₂ − y₁)/(x₂ − x₁) and shows the working so you can check each step by hand.
Is the Extrapolation 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.