Deposit Growth Calculator
Compound interest is the quiet engine of savings: interest earns interest, and the balance snowballs. How fast it grows depends on three things: the rate, how long you leave it, and how often interest is compounded. A 5% account compounded monthly beats the same 5% compounded annually, and regular monthly contributions beat either one alone.
The calculator below handles all of it: a single starting deposit, optional monthly contributions, and five compounding frequencies. It shows the future value, how much of it is your money versus interest earned, the effective annual yield, the doubling time, and a year-by-year growth table.
| Year | Balance | Contributions | Interest earned |
|---|
Estimates only. The math assumes one constant rate, end-of-period contributions, no taxes, no fees, and no withdrawals. Real savings rates move, so treat the result as a planning figure, not a promise.
Quick Answer
- Quick Answer
- The two formulas this calculator runs together
- Worked example: $1,000 down, $200 a month, ten years
- Lump sum or monthly contributions: the comparison the FAQ cannot settle
- How compounding frequency changes the same deposit
- Doubling time: the exact number behind the Rule of 72
- What competing calculators miss
- Frequently Asked Questions
- Add This Calculator to Your Website
- References
The two formulas this calculator runs together
Deposit growth is two calculations added together: the lump sum compounding on its own, and the stream of monthly contributions compounding on its own.
Two modeling choices are baked into that second formula, and both are worth knowing before you quote a result. Contributions are treated as end-of-period payments, the standard ordinary annuity assumption, so a contribution made on the first of the month will run slightly ahead of this estimate in a real account. And the monthly amount is converted to a per-period payment by dividing the yearly total by the number of periods, which is what lets one contribution input work cleanly with all five frequencies, from annual to daily. If your interest is in the daily end of that range on its own, the daily compound calculator works in day counts with daily deposits instead of monthly ones.
The yield line deserves a sentence of its own. Under Regulation DD, the Truth in Savings rules at 12 CFR Part 1030, US banks must disclose APY using a standard formula, and the calculator's effective annual yield is that same quantity: (1 + r/n)n − 1. It is the one number that lets you compare a monthly compounding account against a high yield savings account quoted on a different schedule.
Worked example: $1,000 down, $200 a month, ten years
The calculator is pre-filled with this case. Every figure below is what it returns, including the full year-by-year table it builds.
| Year | Balance | Contributions so far | Interest earned so far |
|---|---|---|---|
| 1 | $3,506.93 | $3,400.00 | $106.93 |
| 3 | $8,912.14 | $8,200.00 | $712.14 |
| 5 | $14,884.58 | $13,000.00 | $1,884.58 |
| 7 | $21,483.77 | $17,800.00 | $3,683.77 |
| 10 | $32,703.47 | $25,000.00 | $7,703.47 |
Read the interest column as the story of compounding waking up. After year 1, interest is $106.93, a rounding error next to the $3,400 contributed. By year 10 the interest earned in that single stretch of the table is larger than the first five years combined, because the balance doing the earning is now mostly other people's money: contributions plus earlier interest. The same table at a 0% rate is a useful control: the balance climbs in flat $2,400 yearly steps to exactly $25,000.00, which proves the $7,703.47 gap at 5% is interest and nothing else. A saver running the habit without a lump sum at all can cross-check the contribution side on the daily savings calculator, which breaks the same discipline down by day.
Lump sum or monthly contributions: the comparison the FAQ cannot settle
Both help, and the calculator lets you price each one separately by zeroing the other. At the same 5% rate, monthly compounding, and 10 year horizon, the two pure strategies land far apart.
Lump sum only
$8,235.05$5,000 deposited once, no contributions. Interest earned: $3,235.05. Every dollar works for the full ten years, but there is only one deposit doing the work.
Contributions only
$31,056.46No starting deposit, $200 a month. You contribute $24,000.00 and earn $7,056.46. The later deposits compound for less time, yet the sheer count of them wins easily.
Both together
$32,703.47The worked example: $1,000 down plus $200 a month. Contributions supply $25,000.00 of the total; compounding adds $7,703.47 on top.
The practical reading is not that lump sums are weak. It is that a contribution habit manufactures new principal every month, and principal is the raw material compounding needs. If a windfall arrives, depositing it early still beats holding it back to drip in later, because the formula pays for time in the account, not for good intentions.
How compounding frequency changes the same deposit
Frequency is the smallest lever of the three, and this calculator is one of the few that lets you move it while holding everything else still. Set contributions to zero and the initial deposit to $10,000 at 5% for 10 years, and the five settings give five different answers to the same question.
| Compounding | Future value | Interest earned | Effective annual yield |
|---|---|---|---|
| Annually | $16,288.95 | $6,288.95 | 5.000% |
| Semiannually | $16,386.16 | $6,386.16 | 5.062% |
| Quarterly | $16,436.19 | $6,436.19 | 5.095% |
| Monthly | $16,470.09 | $6,470.09 | 5.116% |
| Daily | $16,486.65 | $6,486.65 | 5.127% |
The whole spread from worst to best is $197.70 on a $10,000 deposit over a decade. That is real money, and worth taking when two accounts are otherwise equal, but it is smaller than a 0.25 percentage point difference in the stated rate would make. Compare accounts on the yield column first and the frequency column second. The SEC's investor education site makes the same comparison available with its own compound interest calculator at Investor.gov, a good independent cross-check on any figure here.
Doubling time: the exact number behind the Rule of 72
The result box prints how long money takes to double at your rate and frequency, computed exactly as ln(2) divided by (n × ln(1 + r/n)). For the worked example, 5% compounded monthly, that is 13.9 years.
The famous shortcut, divide 72 by the rate, gives 14.4 years at 5%: close, and fine for a conversation, but it is an approximation tuned for annual compounding at middling rates. This calculator's figure accounts for your actual frequency, which is why daily compounding at the same 5% also prints 13.9 years while annual compounding prints 14.2. If doubling time is the question you actually came with, the compound interest doubling time calculator is built around that single number.
What competing calculators miss
The tools ranking for deposit and savings growth terms are strong on the basic formula, and several add charts. Four gaps kept showing up in that set.
Miss 1: contributions or frequency, rarely both. One ranking savings tool fixes compounding at monthly and builds its whole formula around that single schedule. Another compounds annually only. Here the monthly contribution and all five frequencies coexist, so the $197.70 frequency spread and the contribution effect can be priced in the same session.
Miss 2: no year-by-year table, or a table without the split. A final balance alone hides the only interesting question, when interest starts outrunning deposits. The table here separates balance, cumulative contributions, and cumulative interest for every year, which is what makes the year 1 figure of $106.93 against year 10 momentum visible at all.
Miss 3: APY quoted, doubling time missing. Most competitors show an effective yield and stop. The doubling line answers the question savers actually ask out loud, how long until this doubles, and answers it exactly for the chosen frequency instead of with the Rule of 72.
Miss 4: silent contribution timing. Tools that accept monthly contributions almost never say when those contributions are assumed to land. This page states it in the formula section and the FAQs: end of period, spread evenly across periods. A tool that hides its timing assumption is making a choice for you without telling you.
Disclaimer: this calculator is an educational tool for estimating growth at a constant rate. It is not financial advice, and it does not account for taxes, fees, inflation, penalties, or rate changes. For decisions about saving or investing, consult a qualified financial professional.
Frequently Asked Questions
Future value = P × (1 + r/n)^(n × t), where P is the initial deposit, r the annual rate as a decimal, n the compounding periods per year, and t the years. Regular contributions add the future value of the contribution stream on top: each period's payment × [((1 + r/n)^(n × t) − 1) / (r/n)]. This calculator runs both parts together.
Yes, modestly. More frequent compounding means interest starts earning interest sooner. On $10,000 at 5% for 10 years with no contributions, daily compounding gives $16,486.65 against $16,288.95 for annual compounding, a difference of $197.70. The rate, the contributions, and the time matter far more.
The rate is the nominal annual figure; APY (annual percentage yield) folds in compounding frequency. A 5% rate compounded monthly is a 5.116% APY, and compounded daily it is 5.127%. The calculator shows the effective annual yield for your chosen frequency, so compare accounts on that line.
On the numbers in this calculator, steady contributions usually win because there are so many of them. At 5% compounded monthly for 10 years, a $5,000 lump sum with no contributions grows to $8,235.05, while $200 a month with no lump sum reaches $31,056.46. The worked example combines a $1,000 start with $200 a month and reaches $32,703.47. Money deposited earlier compounds longer, so doing both beats either alone.
The calculator computes it exactly for your rate and frequency: doubling time = ln(2) / (n × ln(1 + r/n)). At 5% compounded monthly that is about 13.9 years. The Rule of 72 gives a quick estimate, 72 / 5 = 14.4 years, close but not exact.
The math is identical for a fixed-rate CD held to maturity: a single deposit, a fixed rate, and a chosen compounding schedule. Enter the CD's term and rate with contributions set to zero to project its maturity value. Early withdrawal penalties are not modeled.
The calculator spreads each month's contribution evenly across the compounding periods and treats it as an end-of-period payment, the standard ordinary annuity assumption. There is no start-of-period option, so if your account credits contributions on the first of the month, your real balance will run slightly ahead of this estimate.
Exactly your contributions and nothing more. With the worked example inputs at 0%, the future value is $25,000.00, interest earned is $0.00, and the year-by-year table climbs in straight $2,400 steps. It is a useful sanity check on the contribution math.
No. It projects growth at one constant rate and ignores taxes, account fees, and inflation, all of which reduce a real return. For a conservative plan, rerun it with a slightly lower rate than the advertised one and treat that lower result as your working figure.
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References
- U.S. Securities and Exchange Commission, Investor.gov, "Compound Interest Calculator" - the SEC's own growth calculator and its explanation of how compounding frequency changes returns. SEC Investor.gov: Compound Interest Calculator. Accessed October 2026.
- U.S. Securities and Exchange Commission, Investor.gov, "Savings Goal Calculator" - the contribution side of savings planning, used to frame the lump sum versus contributions comparison. SEC Investor.gov: Savings Goal Calculator. Accessed October 2026.
- Consumer Financial Protection Bureau, Regulation DD (Truth in Savings), 12 CFR Part 1030 - the federal rule requiring standardized APY disclosure for deposit accounts. CFPB: Regulation DD, 12 CFR Part 1030. Accessed October 2026.
- Consumer Financial Protection Bureau, Appendix A to Part 1030, "Annual Percentage Yield Calculation" - the official APY formula behind the effective annual yield line. CFPB: Appendix A to Part 1030, APY Calculation. Accessed October 2026.
- Electronic Code of Federal Regulations, Title 12, Part 1030, "Truth in Savings (Regulation DD)" - current regulatory text covering daily balance and average daily balance methods. eCFR: 12 CFR Part 1030, Truth in Savings. Accessed October 2026.
- Bankers Online, Regulation DD Section 1030.7, "Payment of interest" - the rule text on how interest is calculated and credited on deposit accounts. Bankers Online: Regulation DD 1030.7, Payment of Interest. Accessed October 2026.
- Federal Reserve Bank of St. Louis, FRASER archive, "Final Regulation DD (Truth in Savings)" - the original Federal Reserve rulemaking record for deposit yield disclosure. FRASER: Final Regulation DD (Truth in Savings). Accessed October 2026.
- Capital One, "APR vs. APY: What's the Difference?" - a plain language comparison of borrowing APR and deposit APY, including why compounding lifts APY above the stated rate. Capital One: APR vs. APY. Accessed October 2026.
- Federal Deposit Insurance Corporation, "National Rates and Rate Caps" - the FDIC's published national average deposit rates, the benchmark for judging whether a savings rate is competitive. FDIC: National Rates and Rate Caps. Accessed October 2026.