How it works
Project compound growth of a lump sum with optional regular contributions, and see the year-by-year breakdown.
Enter an initial amount, an annual interest rate, a duration and how often interest compounds. You can add a regular contribution at monthly, quarterly or annual frequency, deposited at the beginning or the end of each contribution period. The simulation runs one compounding period at a time, so the totals always reconcile with the year-by-year table. When contributions are more frequent than compounding (for example monthly deposits with annual compounding), the deposits inside one compounding period are credited together at the end of that period and earn no interim interest — the table shows exactly what happened.
Formula
Lump sum: FV = P × (1 + r)^n. Ordinary contributions (end of period): FV = PMT × ((1 + r)^n − 1) ÷ r; beginning-of-period contributions multiply that annuity by (1 + r). r = annual rate ÷ compounding periods per year and n = years × compounding periods.
P- Initial amount (currency)
PMT- Regular contribution per contribution period (currency)
r- Interest rate per compounding period (annual % ÷ periods)
n- Number of compounding periods (periods)
Examples
- 10,000 at 6% for 10 yearsInitial 10,000 · rate 6% · 10 years · monthly compoundingFinal balance ≈ 18,193.97 · interest ≈ 8,193.97
- 10,000 plus 200 per monthInitial 10,000 · contribution 200 · monthly · end of period · rate 6% · 10 yearsFinal balance ≈ 50,969.84 · contributed 34,000 · interest ≈ 16,969.84
Frequently asked questions
What is the difference between beginning and end of period?
A beginning-of-period deposit starts earning interest one period earlier, so it grows slightly more. End-of-period deposits are added after that period's interest. Both are shown for the same contribution.
What if contributions are more frequent than compounding?
Deposits made inside one compounding period are credited together at the end of that period and do not earn interim interest. This is stated so the result is not over-stated. Beginning-of-period timing is therefore not available for that combination.
Why is monthly compounding higher than annual?
With the same annual rate, interest is added more often, so it starts earning interest earlier. The difference is shown directly when you switch the compounding frequency.
Are these investment returns guaranteed?
No. The result is deterministic arithmetic for the rate and contributions you enter; real returns vary and fees, taxes and inflation are not included.
How to read the result
Total contributed is everything you put in (initial amount plus all deposits). Interest earned is the growth on top. The year-by-year table shows how the balance builds: contributions first, then the interest they generate.
Limitations
Assumes a fixed rate for the whole term and no fees, taxes, inflation or withdrawals. It is a projection, not investment advice.
Source: Standard compound-interest and annuity identities; period-by-period simulation for exact contribution timing.