TNDMTANDEM DIABETES CARE INC— $500 a month, backtested
A dollar-cost-averaging backtest: a fixed amount (default $500 a month) invested into this stock on a fixed schedule, over real split- and dividend-adjusted (total-return) prices with dividends reinvested and no fees or taxes, compared against the same schedule into the S&P 500 (SPY) and a day-1 lump sum. Invested principal, end value and the money-weighted annualized return (XIRR) are engine-computed from historical prices, with no LLM. The Plan tab runs entirely in your browser on a return assumption you choose. The backtest is a historical statistic, not a prediction: past performance does not predict future results.
| Ticker | End value | Profit % | annualized (XIRR) |
|---|---|---|---|
| Your basket (TNDM) | $46,917 | -11.5% | -2.8% |
| Same schedule into SPY | $108,508 | +104.7% | +15.8% |
| Lump sum on day 1 (same total, same basket) | $189,921 | — | — |
Backtested 2017-10-10 → 2026-07-30 · 106 of 106 scheduled buys executed
Simulated 2017-10-10 → 2026-07-30 - limited by TNDM's available history (10 years requested).
A dollar-cost-averaging backtest over real split- and dividend-adjusted (total-return) prices: what investing a fixed amount on a fixed schedule would have grown to, with dividends reinvested and no fees, taxes, or fractional-share limits, versus the same schedule into SPY. A disclosed historical statistic - NOT a prediction, a guarantee, or investment advice. Past performance does not predict future results.
S&P 500 long-run average - a neutral starting point, not a forecast for TNDM.
IMPORTANT: The projections generated by this calculator are hypothetical in nature, computed solely from the return assumption you entered. They do not reflect actual investment results and are not guarantees of future results. They exclude taxes, fees, and inflation. This is arithmetic on your inputs - not a Tickwind forecast or investment advice.
How this is computed
- A contribution of your amount is made at the start of every month (plus the optional initial lump sum at month 0).
- The balance compounds monthly at (1+r)^(1/12) − 1, where r is the annual return you set above.
- The variance band, when enabled, re-runs the same arithmetic at r ± your chosen width - it is not a statistical confidence interval.
How the backtest works
- A fixed amount on a fixed schedule. Each monthly or weekly contribution is split across the basket at fixed weights and buys at that day’s adjusted close (fractional shares, no fees or taxes). There is no rebalancing: the basket drifts with performance, exactly like a real fixed-split auto-invest plan.
- Total return, not price-only. Prices are split- AND dividend-adjusted, so every curve already includes reinvested dividends.
- Buys execute on the first common trading day at or after each scheduled date across every basket ticker and SPY; a slot with no trading day of its own is skipped and disclosed - money is never silently doubled up.
- annualized (XIRR) is the money-weighted annual return that makes the dated contributions grow to the end value - the honest rate for a stream of contributions, where a simple CAGR would be wrong. It is omitted (—) on windows under a year rather than annualized misleadingly.
- The SPY row applies the identical schedule to the S&P 500 ETF; the lump-sum row shows the same total invested in the same basket on day 1 - the classic DCA-versus-lump-sum comparison, disclosed instead of implied.
- A historical backtest, not a forecast. A stat that cannot be computed honestly shows "—", never a fabricated 0. Past performance does not predict future results.
The backtest on this page is a disclosed historical statistic over real prices; the plan is hypothetical arithmetic on your inputs. Neither is a prediction, a price target, or investment advice. Past performance does not predict future results.