Savings Calculator — Goal Growth, Tax & Inflation
See how savings grow from an initial deposit and regular contributions, with after-tax growth, inflation-adjusted value, doubling time and a yearly ledger.
A clear path from inputs to results.
Watch a savings balance grow from an opening deposit plus regular contributions, with the interest rate, compounding, taxes and inflation all made explicit. The results show the nominal value, what it is worth in today's money, how much went in versus what interest earned, and how long doubling takes.
How to use
- Enter the initial deposit — what is in the account today.
- Set the regular contribution and its frequency; weekly, biweekly, monthly, quarterly or annual amounts are converted to a level monthly rate.
- Enter the APY your bank quotes, the number of years, and the compounding frequency.
- Enter your marginal tax rate if the interest is taxable — the engine grows the balance at the after-tax rate APY × (1 − tax) and tracks the tax paid.
- Toggle the inflation view to see the future balance deflated into today's dollars at your assumed inflation rate.
- Read the future value, the principal-versus-interest split, the doubling time and the year-by-year ledger.
The formula
Reference: Monthly-compounded future value with level deposits (compound interest combined with the future value of an annuity; Broverman, Mathematics of Investment and Credit). Doubling time uses the Rule-of-72 approximation 72 ÷ rate; the real value deflates the balance by (1 + inflation)^(years).
Worked example
$10,000 to start, $500 a month, 7% APY for 20 years
- Initial deposit $10,000; contribution $500 monthly; APY 7%; 20 years; monthly compounding; 0% tax; inflation view at 3%.
- 1
The monthly growth rate is 7% ÷ 12 = 0.5833%. Each month the balance earns that rate and then receives the $500 deposit. After 240 months the balance is $300,850.72: $130,000 of deposits ($10,000 initial plus $120,000 contributed) and $170,850.72 of interest — interest out-earns everything you put in. The Rule of 72 puts doubling at 72 ÷ 7 ≈ 10.3 years. Switching on the 3% inflation view deflates the balance to $166,573.75 in today's purchasing power.
Balance $300,850.72 after 20 years ($130,000 principal plus $170,850.72 interest); doubling time about 10.3 years; $166,573.75 in today's dollars at 3% inflation.
Interpreting the result
The principal-versus-interest split is the motivator: past the midpoint of a long horizon, interest contributes more than your deposits. The real-value line is the honest one for goal setting — $300,850.72 in 20 years buys what $166,573.75 buys today at 3% inflation. The doubling time shows what a lower APY costs: drop the rate to 5% and 72 ÷ 5 stretches doubling to about 14.4 years.
Assumptions & limitations
- The APY is constant over the whole horizon; real savings rates move with the market and account tiers.
- Contributions are converted to a level monthly amount (frequency × amount ÷ 12) and credited after each month's interest.
- Tax is modeled as a flat rate on gross interest each month, with growth applied at the after-tax rate; tax-advantaged accounts can use 0%.
- Inflation is a single flat rate applied over the full term; the real value is the nominal balance deflated by (1 + inflation)^(years).
- The projection is capped at 100 years; results are gross of account fees.
Frequently asked questions
How much will $500 a month grow to in 20 years at 7%?
With a $10,000 head start, $300,850.72 — of which only $130,000 is money you deposited and $170,850.72 is interest. The same $500 deposits without the head start reach about $260,463, so the opening deposit adds roughly $40,388 by itself over 20 years.
How much does tax drag cost?
Taxing interest at 25% turns a 7% APY into a 5.25% net rate. On the worked example the 20-year balance falls from $300,850.72 to $240,067.03 — $60,783.69 less — even though the tax actually paid totals $36,689.01; the rest of the gap is interest the taxed-away money would itself have earned.
Is the APY input the same as what the bank quotes?
With the default monthly compounding, yes: the balance grows by exactly your APY over each full year. If you change the compounding frequency, the engine treats your entry as a nominal annual rate divided across those periods, so a daily setting compounds to slightly more than the quoted figure. Match the frequency to how your account actually credits interest.
What is the Rule of 72?
A quick mental shortcut: divide 72 by your annual rate to get the approximate doubling time in years — 72 ÷ 7 ≈ 10.3 years at 7%. The tool computes it from your after-tax rate, so a 7% APY taxed at 25% doubles in 72 ÷ 5.25 ≈ 13.7 years, not 10.3.
What will my balance be worth in today's dollars?
Turn on the inflation view: at 3% inflation the $300,850.72 balance deflates to $166,573.75 of today's purchasing power. Planning in real dollars keeps the target honest — a number that grows nominally may buy far less by the time you reach it.
Can I model quarterly or annual deposits?
Yes — set the contribution frequency next to the amount. The engine converts it to an equivalent level monthly deposit (for example, $1,500 quarterly becomes $500 a month), which keeps the growth math continuous. Real accounts credit deposits on their own dates, so treat the schedule as a close approximation.
Methodology last reviewed 2026-10-06. Results are informational and not financial or engineering advice — see our disclaimer.