How this calculator works
The opening balance earns interest every period. Each deposit arrives at the period end and starts earning interest in the following period. Deposits and compounding use the same frequency. The rate stays fixed; tax, fees, withdrawals and inflation are excluded.
Formula
i = r/m; F = P(1+i)^N + C((1+i)^N - 1)/i. At i = 0, F = P + NC. Contributions = P + NC; interest = F - contributions. P is the opening balance, C the deposit, r the nominal annual rate as a fraction, m periods per year and N elapsed periods.
Worked example
Start with $10,000, add $100 at each month end and use a 6% nominal annual rate compounded monthly. After 120 months, the balance is $34,581.90: $22,000 contributed and $12,581.90 interest.
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Frequently asked questions
How do I enter a horizon in years?
Multiply years by periods per year. For five years of monthly deposits, enter 12 periods per year and 60 periods.
Can I use a negative rate?
Yes, down to -99% nominal annually. A negative rate reduces the balance, so interest earned can be negative. An account fee is a separate cash flow and is not modelled here.
Does this apply TFSA or RRSP rules?
No. It projects account growth without contribution limits, deductions, grants or tax on withdrawals.