What If You Invested $100 a Month in Bitcoin? How to Work It Out
"What if I had put $100 a month into Bitcoin?" is one of the most searched investing questions. The answer changes every day with the Bitcoin price, so rather than quote a number that will be out of date tomorrow, this guide shows exactly how to calculate it — and what really drives the result.
The calculation
Every month you invest $100 at that month's price:
Bitcoin bought that month = $100 ÷ price that month
Add up every month's Bitcoin, then multiply by today's price:
Value today = Total BTC accumulated × current price
Your profit is that value minus the total you invested ($100 × number of months).
Run your own numbers with the free calculator: Crypto DCA Calculator
Open calculator →A simplified example
To see the mechanics, imagine a year with these monthly prices:
| Month | Price | BTC bought |
|---|---|---|
| Jan | $40,000 | 0.002500 |
| Feb | $45,000 | 0.002222 |
| Mar | $35,000 | 0.002857 |
| Apr | $30,000 | 0.003333 |
| May | $38,000 | 0.002632 |
| Jun | $50,000 | 0.002000 |
| Jul | $55,000 | 0.001818 |
| Aug | $48,000 | 0.002083 |
| Sep | $52,000 | 0.001923 |
| Oct | $60,000 | 0.001667 |
| Nov | $65,000 | 0.001538 |
| Dec | $70,000 | 0.001429 |
| Total | 0.026002 BTC |
You invested $1,200. At $70,000, 0.026 BTC is worth about $1,820 — a 51.7% gain. Your average cost was about $46,150 per BTC.
What drives your result
- Start date. Starting just before a long bear market means many purchases at high prices; starting near a bottom means the opposite. Over long periods, the effect shrinks but never disappears.
- Today's price. Your entire accumulated stack is valued at one price, so the result is extremely sensitive to the day you check.
- Volatility along the way. Deep dips while you are buying help; they let your fixed $100 buy more.
- Fees. A 1.5% recurring-buy fee means only $98.50 of every $100 buys Bitcoin. Over ten years that is $180 of fees on $12,000 invested — before counting the growth those dollars could have had.
Use real historical data
The crypto DCA calculator does this calculation with actual monthly or weekly prices. To answer the classic question:
- Choose BTC
- Enter $100
- Choose monthly
- Set your start date — for example, January 2020
- Read the portfolio value, profit, average buy price and the lump-sum comparison
Try different start dates: 2018, early 2020, late 2021 and 2022. Comparing them shows how much the starting point matters.
Things the headline number hides
- The ride. A plan that shows a large gain today may have been down 50% or more at some point along the way.
- Taxes. When you eventually sell, gains are taxable. In the US, purchases held over a year qualify for lower long-term rates.
- Opportunity cost. The same $100 could have gone elsewhere; compare with a broad index fund for perspective.
- Survivorship. Bitcoin is the best-known success; a $100 monthly plan into many other coins from the same era would have lost money.
The real lesson
The value of a $100 monthly plan is less about the exact number and more about the habit: small, regular, automatic investing that does not depend on predicting the market. Model a few scenarios, choose an amount you can keep up through a bear market, and let time do the work.
CryptoMathly provides educational estimates only and is not financial, investment or tax advice. Crypto assets are volatile and you can lose money. Always verify figures with a qualified professional.