Two federal tools model investment growth without selling a product: the SEC's Investor.gov Compound Interest Calculator projects a balance from a starting amount, an assumed rate, and optional periodic deposits, while the US Treasury's TreasuryDirect Savings Bond Calculator reads a specific paper EE, E, or I bond's own recorded schedule to find its actual current value; neither predicts a market return.
What official government investment calculators means
Investor.gov, the SEC's investor-education site, hosts a Compound Interest Calculator that determines how money can grow using a chosen rate and compounding schedule, while TreasuryDirect's Savings Bond Calculator prices paper Series EE, E, and I bonds and savings notes and reports each bond's current interest rate, next accrual date, final maturity date, and interest earned so far. The compound-interest tool answers a what-if question using a rate the user selects; the savings bond calculator answers a what-is-it-worth-now question about one specific, already-issued instrument with its own contractual terms.
| Starting amount | $10,000 |
|---|---|
| Assumed annual return | 6% |
| Horizon | 10 years |
| Projected balance | $17,908.48 |
| EE bond 20-year guarantee | doubles in value |
What official US government investment calculators exist, and what do they compute?: worked numbers
Entering $10,000 with no further deposits, an assumed 6% annual return compounded annually, and a 10-year horizon into a compound-interest projection gives 10,000 x 1.06^10, or about $17,908.48 - a scenario built from a chosen rate, not a forecast. Separately, TreasuryDirect states that an EE bond bought today is guaranteed to double in value in 20 years, even if Treasury has to add money at the 20-year mark to make that happen, so a $1,000 EE bond is guaranteed to be worth $2,000 after 20 years regardless of its stated interest path.
How to calculate official government investment calculators
For a hypothetical projection, apply the compound interest formula future value equals present value times (1 plus the assumed rate) raised to the number of periods, holding the rate constant only as an assumption to test. For an actual paper bond, TreasuryDirect's calculator instead looks up the bond's series, denomination, and issue date and applies that bond's own recorded interest history rather than a single formula.
Use related Calculatort tools when the inputs are known: compound growth projection; retirement savings projection; fund-fee twenty-year impact.
Common mistakes
Do not read a compound-interest projection's assumed rate as a promised or average market return - it is a user-chosen input for comparison, not a guarantee. Do not price an electronic savings bond with the paper-bond calculator; electronic bonds are valued by logging into a TreasuryDirect account instead.
Where the calculation stops
Neither calculator accounts for taxes on interest, state tax treatment of Treasury interest, inflation-adjusted purchasing power, brokerage or fund fees, or the risk and volatility of a stock or bond-fund investment; a savings bond's guarantee also applies to Treasury's own bonds, not to any other product.
official government investment calculators: source and verification
The SEC's Investor.gov hosts the Compound Interest Calculator, and the US Treasury's TreasuryDirect (treasurydirect.gov/savings-bonds/ee-bonds/ and treasurydirect.gov/savings-bonds/savings-bond-calculator/) states that a current Series EE savings bond is guaranteed to double in value in 20 years. Read the named source. This source names the transaction-specific starting amount and the conditions that qualify it.
Use the result as a dated scenario
Recalculate the official government investment calculators case when its listed input changes.
A second Investor.gov input: adding a monthly contribution
The SEC's Compound Interest Calculator does not stop at a single lump sum entered once; it also accepts a recurring contribution alongside the starting amount, which turns the arithmetic into a lump sum plus an ordinary annuity rather than one future-value step. Suppose a saver starts with $2,000, adds $200 at the end of every month, and enters an assumed 6% annual return compounded monthly for 10 years (120 months). The monthly rate is 6% divided by 12, or 0.50%.
The starting $2,000 grows on its own to $2,000 times 1.005 to the power 120, or about $3,638.80. The 120 monthly deposits grow under the ordinary-annuity formula - contribution times [(1 plus rate) to the number of periods, minus 1, divided by rate] - which is $200 times [(1.005^120 minus 1) divided by 0.005], or about $32,776.00. Adding the two streams gives a modeled ending balance of about $36,414.80, still built from the same chosen 6% assumption as the single-lump-sum case, not a promised return.
What a real I bond's own composite-rate formula looks like
TreasuryDirect's EE bond guarantee is not the only official bond-rate arithmetic worth checking against its source. Series I savings bonds combine a fixed rate that holds for the bond's 30-year life with an inflation-linked rate that resets every May 1 and November 1, using the formula the Bureau of the Fiscal Service publishes: composite rate equals fixed rate, plus 2 times the semiannual inflation rate, plus the fixed rate times the semiannual inflation rate.
For I bonds issued from November 1, 2025 through April 30, 2026, Treasury's November 2025 rate announcement set a 0.90% fixed rate and a 1.56% semiannual inflation rate. Reproducing the formula: 0.0090 + (2 times 0.0156) + (0.0090 times 0.0156) = 0.0090 + 0.0312 + 0.00014 = 0.04034, which matches the announced 4.03% composite rate for the first six months those bonds are held. Six months earlier, the May 2025 announcement had set a higher 1.10% fixed rate paired with a lower 2.86% semiannual inflation component, for a 3.98% composite - proof that buying in a different six-month window changes both inputs and the resulting rate, even for the same 30-year bond series.
Three official tools, three different questions
| Tool | Publisher | What it computes | What resets and when |
|---|---|---|---|
| Compound Interest Calculator | SEC Investor.gov | a projection from a chosen rate, starting amount, and optional monthly contributions | nothing - the rate stays whatever the user assumes |
| Savings Bond Calculator (paper EE/E/I) | TreasuryDirect | the current redemption value of one already-issued paper bond | reads that bond's own recorded interest history |
| I bond composite rate | Bureau of the Fiscal Service | the rate applied to I bonds issued within a six-month window | every May 1 and November 1 |
The dispute this guide resolves: which bond is guaranteed to double
TreasuryDirect's 20-year doubling guarantee is written into the terms of Series EE bonds only; it does not extend to Series I bonds, whose composite rate resets twice a year with no comparable promise. A saver who reads the EE bond page and then assumes the same guarantee covers an I bond purchase is applying one instrument's contractual terms to a different one - both are priced on the same TreasuryDirect site, but only the EE bond's own page states the doubling guarantee, and only the I bond's own page publishes the twice-yearly composite-rate formula used above.
Checking the annuity total by splitting it back apart
To verify the $36,414.80 modeled balance from the first section, split the two streams and check each alone: the lump-sum leg by itself, $2,000 times 1.005^120, must return $3,638.80 on its own, and the annuity leg by itself, with no starting deposit, must return $32,776.00 on its own. A spreadsheet's built-in future-value function - FV(0.005, 120, -200, -2000) - should reproduce the same combined total; a mismatch usually means the contribution timing (end of month versus start of month) or the compounding frequency was set differently than assumed here.