MihsabaHow to use
Linear interpolation estimates a value on the straight line through two known points. A target x between x₁ and x₂ is interpolation; a target outside the interval is extrapolation and usually deserves more caution.
- Enter known points (x₁,y₁) and (x₂,y₂).
- Enter the target x.
- Review y, slope, position fraction and calculation type.
How it is calculated
y=y₁+(x−x₁)(y₂−y₁)÷(x₂−x₁)
Example
Between (0,10) and (20,50), x=5 gives t=0.25 and y=10+0.25×40=20.
Important notes
The method assumes a straight-line change between the two points. Real data may not be linear, and extrapolation outside the known range is generally less reliable.
Frequently asked questions
What if x₁ equals x₂?
The formula has a zero denominator, so the calculator rejects that vertical-line case.
Does it allow extrapolation?
Yes, but the result is explicitly flagged as outside the interval.
What is t?
It is the relative x position: 0 at the first point and 1 at the second.
Is this calculator free?
Yes. It is free to use and requires no account.