Basic Interest Calculator
Basic interest calculator works out Interest and Final amount from Principal, Annual interest rate and Time (years). The default figures on this page give interest of 100.00; change any entry and the result, the working and the sources update together.
Your figures
Updates as you typeHow this is worked out
3 steps
- Term in years t = 2 + 0/12 + 0/365 = 2
- I = P x (r/100) x t = 1000 x (5/100) x 2 = 100
- A = P + I = 1000 + 100 = 1100
Its 5 worked examples are re-run on every release, last on 15 September 2026. What changed
Sources and references
2 sources
Keep this result
Save it, change one figure, then compare the two
The calculation stays free. Save this scenario, adjust one assumption, save that too, and put them side by side to see exactly what the change costs you. A free account keeps 5 scenarios and 2 comparisons; Personal makes both unlimited and adds exports and private links. Nothing is saved unless you press Save.
What the basic interest calculator calculates
Computes simple, non-compounding interest and the final amount from a principal, an annual rate and a term given in years, months or days, and rearranges the same equation to solve for the rate, the principal or the time.
How to use this basic interest calculator
Enter Principal, Annual interest rate, Time (years) and Time (extra months). Interest updates as you type, and “Use a worked example” loads checked figures you can adjust. Change one figure at a time to see what drives the result.
How the result is worked out
Open “How this is worked out” beside the result for the step-by-step calculation behind Interest, Final amount and Principal.
The method follows OpenStax, Elementary Algebra 2e - simple interest and proportional relationships and US Treasury Financial Manual - ordinary (360-day) and exact (365-day) interest bases.
Research R3057-GT-1: 1,000 at 5% for 2 years example
With Principal: 1000, Annual interest rate: 5, Time (years): 2, the calculator returns Interest: 100, Final amount: 1100. This example is checked against an independent source in the test suite.
What you can compare
Change one input at a time to see how it affects Interest, Final amount and Principal. The inputs you can vary are Principal, Annual interest rate, Time (years), Time (extra months), Time (extra days) and Days in a year.
Results are general information, not financial, tax, legal, medical or engineering advice. Check any decision that matters with a qualified professional.
See something wrong? Report a problem with this calculator
Frequently asked questions
What is 5% interest on $50,000?
Computes simple, non-compounding interest and the final amount from a principal, an annual rate and a term given in years, months or days, and rearranges the same equation to solve for the rate. On this page it is computed from Principal, Annual interest rate and Time (years) and shown as Interest, Final amount and Principal.
What is the 2% interest of 10,000?
On the figures this page opens with — principal 1,000, annual interest rate 5 percent/year and time (years) 2 years — the interest is 100. No single number fits everyone: change any figure above and the answer updates as you type, with each step of the arithmetic beside it.
What information do I need for the basic interest calculator?
You need Principal, Annual interest rate, Time (years), Time (extra months), Time (extra days), Days in a year, Interest amount and Solve for. The page opens with default figures that give interest of 100.00, so you can see the scale before entering your own.
What does this basic interest calculator show?
It shows Interest, Final amount, Principal, Annual rate, Time, Interest per day and Interest per month, with the working and any warnings for your entries.
Can I check how the basic interest calculator result was calculated?
Yes. The “How this is worked out” section shows the calculation steps, and the sources section identifies the references used for the method.