You can estimate “how much interest will I earn” with two main formulas, depending on whether the account uses simple or compound interest. Here’s a clear guide you can plug your own numbers into.

1. Simple interest (rare for savings)

Use this if interest is paid only on your original deposit (principal), not on previous interest.

Formula

Interest=P×R×T\text{Interest}=P\times R\times TInterest=P×R×T

  • PPP: principal (your starting balance)
  • RRR: annual interest rate as a decimal (3% → 0.03)
  • TTT: time in years

Example (you can swap in your numbers):

  • P=1,000P=1{,}000P=1,000
  • R=0.05R=0.05R=0.05 (5%)
  • T=3T=3T=3 years

Interest=1,000×0.05×3=150\text{Interest}=1{,}000\times 0.05\times 3=150Interest=1,000×0.05×3=150

So you’d earn 150 in interest over 3 years and end with 1,150.

2. Compound interest (most common for savings)

Most savings accounts compound daily, monthly, or annually, which means you earn interest on your interest.

Formula for ending balance

A=P(1+rn)ntA=P(1+\frac{r}{n})^{nt}A=P(1+nr​)nt

  • AAA: amount after time ttt
  • PPP: starting balance
  • rrr: annual interest rate as a decimal
  • nnn: number of compounding periods per year (12 for monthly, 365 for daily, 1 for annual)
  • ttt: years

Interest earned = A−PA-PA−P.

Example (monthly compounding)

  • P=1,000P=1{,}000P=1,000
  • r=0.05r=0.05r=0.05 (5%)
  • n=12n=12n=12
  • t=3t=3t=3

A=1,000×(1+0.0512)12×3A=1{,}000\times (1+\frac{0.05}{12})^{12\times 3}A=1,000×(1+120.05​)12×3

If you calculate that, you get about 1,161. So interest ≈ 161 over 3 years.

3. Step‑by‑step: figure out your interest

To answer “how much interest will I earn” for your own situation, gather:

  1. Your starting balance (principal).
  2. The annual interest rate (APR or APY).
  3. How often interest is compounded (daily, monthly, yearly).
  4. How long you’ll keep the money there (in years).

Then:

  • If it’s simple interest, use P×R×TP\times R\times TP×R×T.
  • If it’s compound, use A=P(1+r/n)ntA=P(1+r/n)^{nt}A=P(1+r/n)nt and compute A−PA-PA−P.

Many bank or financial websites also offer free “interest calculators” where you enter these numbers and they compute the result for you.

4. Mini example with deposits

If you plan to add money regularly (like monthly deposits), use an online “savings interest calculator” that lets you enter: starting balance, monthly contribution, years, and interest rate. It will show total interest earned and your future balance.

If you tell me:

  • your balance (or planned deposits),
  • the rate (e.g., 4.5% APY),
  • how often it compounds,
  • and how long you’ll save,

I can walk you through the exact interest you’d earn using your numbers.
Information gathered from public forums or data available on the internet and portrayed here.