Tool: Simple interest calculator · Embed · All how-we-calculate pages · Questions
Purpose
Estimate interest and total amount when interest is charged or earned on principal only (no compounding), using a constant annual rate and time in years that you type. Educational only.
Core formulas
- Interest:
I = P × r × t - Total amount:
A = P + I -
P= principal,r= annual rate as a decimal (e.g. 5% → 0.05),t= time in years (can be fractional)
Year schedule
For whole years, we list interest and total to date at each integer year using the same formula with
t = 1, 2, …. If years is fractional, the final row uses the full t you entered.
Simple vs monthly compound (contrast only)
The calculator also shows monthly-compound interest on the same P, r, and t using
A = P(1 + r/12)^(12·t) so learners can see that compounding earns interest on prior interest. This
is a teaching contrast—not a product quote.
What we intentionally leave out
- Fees, taxes, penalties, and day-count conventions (e.g. 360/365)
- Live bank or lender rates
- Amortization schedules or minimum payments
- Investment performance forecasts
Related
Last reviewed: August 9, 2026.
YMYL notice: This site is for education only. It is not financial, tax, or investment advice. Nestfigure is not a bank, credit union, broker, investment adviser, or fiduciary. Product terms, rates, and penalties vary—always read your institution’s disclosures before acting. Calculator results are mathematical estimates, not bank quotes.