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Learn the best principles to negotiate the salary you deserve!

Machine Design

How-to, in-depth technical articles for machine design engineers

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Gear drives, bearings, motors, clutches, couplings, machine controls, sensors and components.

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Scenario 1: Find the Monthly Payment

Loan Amount (C)

Interest Rate % (R)

Number of Months (N)

Monthly Payment (P): 
Interest rate R% is always a yearly figure. However, in most loan situations it is compounded monthly. In this calculator the monthly payment is calculated by the following formula where r = R/1200:
Scenario 2: Find the Interest Rate

Loan Amount (C)

Monthly Payment (P)

Number of Months (N)

Interest Rate % (R): 
For given C, P and N, one can only solve the following equation for r by numerical means.
Given the rather smooth behavior of this equation, this calculator employs the Newton-Raphson method with an educated initial guess:
Scenario 3: Find the Number of Payments

Loan Amount (C)

Interest Rate % (R)

Monthly Payment (P)

Number of Months (N): 
This calculator figures out the number of months N by the following closed-form expression:
Notice that N has to be an integer, so the monthly payment P might be slightly adjusted to satisfy this condition.
Glossary