Compound interest calculator
Project account growth with compounding and repeated contributions.
What this calculator covers
Project how a balance can grow over time when interest compounds and contributions keep getting added.
This page is designed to explain where the ending balance comes from instead of only showing a final total.
Frequently asked questions
- How often is interest compounded here?
- You choose the compounding frequency — yearly, quarterly, monthly, daily, or continuous. More frequent compounding produces a slightly higher final balance for the same stated annual rate.
- What's the difference between simple and compound interest?
- Simple interest is paid only on the original principal. Compound interest is paid on the principal plus any interest that's already been earned, which is why compound growth accelerates over longer time horizons.
- Can I include regular contributions?
- Yes — when you enter a recurring contribution, the projection applies it at the chosen interval and compounds the growing balance through the remaining term. Set the contribution to zero to model a single lump sum.
- What annual return should I use for planning?
- For conservative planning, many people model 4%–6%. Historical long-run stock-heavy portfolios have averaged closer to 7% after inflation, but past performance doesn't guarantee future results. Run multiple scenarios to see the range of outcomes.
Tool
Run the calculation
Result
RESULT · COMPOUND INTEREST
â„–008
Primary result
$31,998.32
$10,000.00 growing at 5% for 10 years reaches $31,998.32 with the current contribution plan.
- Ending balance
- $31,998.32
- Total contributions
- $12,000.00
- Interest earned
- $9,998.32
Step-by-step solution
- 1.Convert the annual rate into a periodic rate: 5% ÷ 12 = 0.004167.
- 2.Count the compounding periods: 10 × 12 = 120.
- 3.Grow the starting principal and the repeated contributions through all periods to reach $31,998.32.
Walkthrough
Visual walkthrough
Compound growth comes from the starting principal, the periodic rate, and the repeated contributions added along the way.
01
Find the periodic rate
5% ÷ 12 = 0.004167
Compounding happens per period, so the annual rate must be broken into matching pieces.
02
Count every compounding event
10 × 12 = 120
That period count determines how many times both the principal and the added contributions can grow.
03
Read the future value
The final balance includes the original deposit, every contribution, and the interest earned on both over time.
Ending balance $31,998.32