What this calculator does
Project a future value from a starting amount, annual rate, time horizon, and optional regular contributions. Results separate money contributed from modeled interest.
Money & Finance · Compound growth
Compound Interest Calculator
Calculate compound interest from a starting amount, annual rate, time, and optional regular contributions. Compare daily through annual compounding and see how much comes from contributions versus interest.
Ready to calculate
Projection inputs and assumptions
Growth over time
| Period | Elapsed years | Contributions this period | Interest this period | Ending balance | Cumulative contributions | Cumulative interest |
|---|
What compound interest means
Compound interest means growth is applied to the existing balance, so previously earned interest can itself earn additional interest.
Compound interest formula
For a lump sum with a nominal annual rate, the standard formula is A = P(1 + r/n)nt, where P is principal, r is the annual rate, n is compounds per year, and t is years.
Daily vs. monthly compounding
At the same positive nominal annual rate, more frequent compounding increases effective annual yield. Daily, weekly, monthly, quarterly, semiannual, and annual options are available.
Regular contributions
Add monthly, quarterly, semiannual, or annual contributions. Beginning-of-period contributions have more time to grow than otherwise identical end-of-period contributions.
Nominal rate vs. APY
A nominal annual rate needs a compounding frequency. APY already expresses effective annual growth, so compounding frequency is not applied again in APY mode.
Reading the result
Future value combines your starting amount, regular contributions, and modeled interest. The growth-over-time table reconciles to the final result.
Savings and investment assumptions
Real savings rates can change and investment returns are not guaranteed. This calculator keeps one constant rate for the full projection.
What is not modeled
Taxes, fees, inflation, withdrawals, changing returns, current product rates, and account-specific crediting rules are outside this calculation.
Browser-local calculations
Your starting amount, rate, time, contribution settings, and projection stay in this active browser page. They are not uploaded for calculation and are not retained as app-owned calculation history after you leave or close the page.
Related Mycelgrid calculators
Use 401K Calculator for salary contributions and employer match, or Mortgage Calculator for fixed-rate borrowing and amortization.
Worked example: daily compounding
$10,000 at a 4% nominal annual rate compounded daily for one year grows to about $10,408.08.
Worked example: monthly contributions
$10,000 plus $200 per month at 5% nominal annual interest compounded monthly for 10 years, with end-of-period contributions, grows to about $47,526.55.
Worked example: contribution timing
Starting from $0, contribute $100 monthly at a 12% nominal annual rate compounded monthly for one year. End-of-period contributions grow to $1,268.25; beginning-of-period contributions grow to $1,280.93. Both scenarios include 12 contributions totaling $1,200, but beginning contributions each have one extra month to grow.
Useful questions
Does daily compounding earn more than monthly?
At the same positive nominal annual rate, yes. More frequent compounding produces a slightly higher effective annual yield.
Can I include monthly contributions?
Yes. Set a Regular contribution and choose Monthly as the contribution frequency.
Does contribution timing matter?
With a positive rate, beginning-of-period contributions generally finish higher because each contribution has more time to grow.
Does this calculator use current bank rates?
No. It uses only the annual rate you enter.
Does it include tax, fees, or inflation?
No. Taxes, fees, and inflation are not included in this calculation.
Read the Compound Interest Formula & Compounding Frequency guide.
