See how your savings grow over time with contributions and compounding
In plain terms: it projects how your savings or investments grow over time as interest earns interest. Enter a starting amount, an optional monthly contribution, an annual rate of return, the number of years, and how often interest compounds, then read your projected future value — split into how much you put in versus how much the compounding earned. Everything runs in your browser: nothing you type is uploaded or stored.
Compound interest calculator shows exactly how your money grows as interest earns interest year after year, turning steady contributions into long-term wealth. Whether you are planning for retirement, building an emergency fund, or projecting the growth of a brokerage account, this tool converts a few simple inputs — your starting deposit, monthly contributions, interest rate, time horizon, and compounding frequency — into a clear picture of your future balance, total contributions, and total interest earned.
Compound interest is often called the eighth wonder of the world because of how quickly it accelerates over time. With simple interest, you earn a fixed amount on your original deposit and nothing more. With compound interest, the interest you earn is added back to your balance, and the next round of interest is calculated on that larger total. In effect, your interest starts earning its own interest — a self-reinforcing cycle that grows faster the longer it runs.
The standard formula for the future value of a lump sum is A = P(1 + r/n)nt, where A is the final amount, P is the principal (your initial deposit), r is the annual interest rate expressed as a decimal, n is the number of times interest compounds per year, and t is the number of years. For example, $10,000 invested at 7% compounded monthly for 30 years grows to roughly $81,165 — more than eight times the original deposit, with over $71,000 of that coming purely from interest.
Compounding frequency determines how often interest is added to your balance. Daily compounding adds interest 365 times a year, monthly adds it 12 times, quarterly 4 times, and annually just once. The more often interest compounds, the sooner it starts earning its own interest, so more frequent compounding always produces a slightly higher final balance at the same stated annual rate. The table below shows the effect on a $10,000 deposit at 5% over 10 years with no additional contributions:
| Compounding Frequency | Periods Per Year | Future Value (10 yrs) | Interest Earned |
|---|---|---|---|
| Annually | 1 | $16,288.95 | $6,288.95 |
| Quarterly | 4 | $16,436.19 | $6,436.19 |
| Monthly | 12 | $16,470.09 | $6,470.09 |
| Daily | 365 | $16,486.65 | $6,486.65 |
Notice how the difference between annual and daily compounding on this deposit is only about $198 over a full decade. Compounding frequency matters, but it is not the lever that transforms your results. The interest rate and — above all — the number of years you stay invested have a much larger impact on your final balance.
Time is the single most powerful ingredient in compound growth. Because the effect accelerates as your balance grows, the earliest dollars you invest do the most work — they have the longest runway to compound. Consider two savers who each invest $5,000 per year at 7%. The first starts at age 25 and stops at 35, contributing for just 10 years. The second starts at 35 and contributes every year until 65, a full 30 years. Remarkably, the early saver who contributed for only 10 years often ends up with a larger balance at 65, despite putting in one-third of the money, simply because their contributions had 30 extra years to compound.
This is why financial educators stress starting as early as possible, even with small amounts. Waiting for a "perfect" moment or a larger paycheck can cost more in lost compounding than the extra contributions would ever make up. A modest amount invested today can outgrow a much larger amount invested a decade from now.
Many people wonder whether it is better to invest a single lump sum or to contribute steadily over time. Mathematically, a lump sum invested at the start always compounds the longest and therefore earns the most per dollar. But most savers do not have a large lump sum available — they build wealth from regular paychecks. The good news is that consistent monthly contributions harness compounding extremely effectively, because each deposit begins growing the moment it is added.
Consider a $10,000 starting deposit at 7% for 30 years. On its own, that lump sum grows to roughly $81,000. Add just $200 per month over the same period and the total climbs to around $308,000 — with the contributions and their compounded growth accounting for the large majority of the final balance. Regular investing also smooths out market timing risk, since you buy at many different price points rather than committing everything at once. For most people, the practical answer is simple: invest whatever lump sum you have now, then keep contributing consistently.
The difference between compound and simple interest is easy to overlook in the short term but enormous over decades. Simple interest is calculated only on your original principal, so it grows in a straight line. Compound interest is calculated on your growing balance, so it curves upward and accelerates. The table below compares a $10,000 deposit at 6% under both methods, with no additional contributions:
| Years | Simple Interest Balance | Compound Interest Balance | Difference |
|---|---|---|---|
| 5 years | $13,000 | $13,382 | $382 |
| 10 years | $16,000 | $17,908 | $1,908 |
| 20 years | $22,000 | $32,071 | $10,071 |
| 30 years | $28,000 | $57,435 | $29,435 |
After 5 years the gap is small — only a few hundred dollars. But by year 30 the compound balance more than doubles the simple-interest balance, and the difference alone exceeds the original deposit. This widening gap is the essence of why long-term investors care so much about compounding: it does its most dramatic work in the final years, precisely when patience pays off most.
Enter your initial deposit, an optional monthly contribution, your expected annual interest rate, the number of years you plan to invest, and how often interest compounds. The calculator projects your future value month by month for accuracy, so contributions are credited at the right time and compounding is applied consistently. Results include your final balance, the total you contributed out of pocket, and the total interest earned, along with a year-by-year breakdown so you can see exactly how the growth curve steepens over time.
Because RapidTools is 100% client-side, every calculation runs privately in your browser. None of the numbers you enter are sent to a server, stored, or shared — your financial figures never leave your device. Keep in mind that this tool assumes a constant interest rate and does not account for taxes, fees, or inflation, so treat its projections as an educational estimate rather than a guarantee. For decisions about specific investments, consult a licensed financial professional.
A projection is only useful if you know what each figure is telling you and the decision it should inform:
When you run the numbers, the calculator also shows a short plain-language summary beneath your results that splits your future value into contributions versus interest and applies the Rule of 72 to your specific rate.
Suppose Alex starts with $5,000, contributes $200 every month, expects a 7% annual return, invests for 30 years, and interest compounds monthly.
Reading that result: Alex contributed roughly $77,000, yet the balance grew to about $285,000 because each month's deposit had years — sometimes decades — to compound. The month-by-month contribution growth is the engine here: it is not one big lump, but many small deposits each riding the compounding curve for their own remaining time.
Once you have a projection, use it to shape a plan rather than just to satisfy curiosity:
A quick reference for the terms you will meet when projecting growth:
Canadians often let compound interest grow inside two registered accounts. In a Tax-Free Savings Account (TFSA), contributions are not tax-deductible, but the interest and other income earned in the account are generally tax-free, even when you take the money out: tax-free growth (canada.ca: What is a TFSA). The TFSA dollar limit for 2026 is $7,000, but your own contribution room can be different, so check it on canada.ca.
In a Registered Retirement Savings Plan (RRSP), contributions can be deducted on your tax return, and income earned in the plan is usually not taxed while it stays there, but you generally pay tax on what you withdraw: tax-deferred growth, where you pay the tax later (canada.ca: RRSP).
This calculator does not include tax. Inside a TFSA, the result is roughly what you keep. Inside an RRSP, withdrawals are taxed. In a regular taxable account, tax on the interest each year means your real growth is lower than shown.
The lump-sum portion uses the standard compound interest formula, A = P(1 + r/n)nt, where P is the principal, r is the annual rate as a decimal, n is the number of compounding periods per year, and t is the number of years. For monthly contributions, the calculator converts your chosen compounding frequency into an effective monthly rate and steps month by month, adding each contribution and applying that month's growth, so deposits are credited at the right time. Total interest is future value minus total contributions. The tool assumes a constant rate and ignores taxes, fees, and inflation, so treat projections as illustrative. All math runs in your browser and no inputs are stored or transmitted.
Formula and guidance last reviewed October 2026. Projections are illustrative and assume a constant rate — they are not guaranteed returns or financial advice. Verify assumptions and consult a licensed professional before investing.
Planning the whole picture? These free, private calculators pair naturally with your compounding math:
Compound interest means you earn interest not only on your original deposit but also on the interest already added to your balance. Each period, interest is calculated on the new, larger balance, so the amount you earn keeps growing. Over long time horizons this snowball effect becomes powerful: a $10,000 deposit at 7% grows to about $19,672 in 10 years and roughly $76,123 in 30 years, with most of that gain coming from interest earning interest rather than the original principal.
Compounding frequency is how often interest is added to your balance — daily (365 times a year), monthly (12), quarterly (4), or annually (1). More frequent compounding earns slightly more because interest starts earning its own interest sooner. On a $10,000 deposit at 5% for 10 years, annual compounding yields about $16,289 while daily compounding yields about $16,487 — a difference of roughly $198. The effect is real but modest; the interest rate and time invested matter far more than frequency.
For a lump sum, future value uses the formula A = P(1 + r/n)^(nt), where P is the principal, r is the annual rate as a decimal, n is the number of compounding periods per year, and t is the number of years. For regular monthly contributions, this calculator steps month by month: it converts your chosen compounding frequency into an effective monthly rate, then each month adds your contribution and applies that month's growth. Summing both the growing principal and the growing stream of contributions gives the total future value.
The Rule of 72 is a quick mental shortcut to estimate how long it takes money to double. Divide 72 by the annual interest rate (as a whole number) to get the approximate number of years. At 6% interest, money doubles in about 72 / 6 = 12 years; at 9% it doubles in about 8 years. The rule is an approximation that works best for rates between roughly 4% and 12%, and it is not a guarantee of returns — actual results depend on the real rate earned.
Adding regular monthly contributions dramatically increases your future value because each deposit begins compounding from the moment it is added. A $10,000 lump sum at 7% for 30 years grows to about $76,123. Adding just $200 per month over the same period adds roughly $227,000 more, for a total near $303,000. Consistent contributions often contribute more to the final balance than the starting deposit, especially over long time horizons.
Simple interest is calculated only on the original principal, so it grows in a straight line: $10,000 at 5% simple interest earns exactly $500 every year, or $5,000 over 10 years. Compound interest is calculated on the growing balance, so it accelerates over time: the same $10,000 at 5% compounded annually earns about $6,289 over 10 years. The gap widens the longer you stay invested and the higher the interest rate, which is why compounding is so valuable for long-term saving.
Yes, more frequent compounding always earns at least as much as less frequent compounding at the same stated annual rate, because interest begins compounding sooner. However, the extra gain shrinks quickly. Moving from annual to monthly compounding produces a noticeable bump, but moving from daily to continuous compounding adds only a tiny fraction more. In practice the stated annual rate and the number of years invested have a far larger impact on your final balance than how often interest compounds.
This calculator uses standard compound interest mathematics and steps month by month for contribution accuracy, so its projections are precise for the assumptions you enter. Real-world results will differ because it assumes a constant interest rate, on-time contributions, and no taxes, fees, or inflation. It is an educational planning tool, not financial advice or a guarantee of returns. For decisions about specific investments, consult a licensed financial professional.
Use it to build a plan, not just to satisfy curiosity. Adjust the monthly contribution until the future value lands on a goal you care about — retirement, a down payment, a college fund — and treat that figure as your savings target. If the projection falls short, the levers within your control are contributing more and starting sooner; reaching for a higher rate usually means taking on more risk. Because the tool ignores taxes, fees, and inflation, use the number to compare scenarios and set direction, then confirm specifics with a licensed financial professional.
Because compounding accelerates as your balance grows, the earliest dollars you invest do the most work — they have the longest runway to earn interest, and then interest on that interest. A saver who invests for just ten years starting in their twenties can end up with more than someone who invests for thirty years starting a decade later, despite contributing far less money. That is why starting earlier and contributing consistently matter more than chasing a slightly higher rate: time in the market is the single most powerful lever in the whole calculation.
Both let savings grow without yearly tax in Canada, but in different ways. A TFSA gives tax-free growth: contributions are not tax-deductible, but the interest and other income are generally tax-free, even when you withdraw. An RRSP gives tax-deferred growth: contributions can be deducted on your tax return, but you generally pay tax when you withdraw. The TFSA dollar limit for 2026 is $7,000, and your own room can be different, so check it on canada.ca.
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