If you buy Bitcoin on autopilot every month, the day you pick matters a little. An analysis of 11 months of price data found that a $100 monthly buy on the 18th stacked 2.28% more Bitcoin than the same buy on the 2nd.
That is the short version. The longer version is more useful: the edge is small, it moves around, and consistency beats timing every time.
How the numbers were computed
We used daily Bitcoin closing prices from Kraken, October 2025 through August 2026. For each day of the month from the 1st to the 28th, we simulated a $100 buy on that day across all 11 months. Total invested per simulation: $1,100. The only variable was the day.
The 18th came out on top with 0.01445 BTC accumulated. The 2nd came last with 0.01413 BTC. At roughly $84,000 per coin, the gap is worth about $27 on $1,100 invested. 
Weekly and hourly: Thursday and 01:00 UTC
Running the same test on weekly $100 buys over 52 weeks, Thursday beat Monday by 1.09%. An hourly test over 30 days put 01:00 UTC on top and 17:00 UTC at the bottom, a 0.44% edge.
Independent research agrees on the size, not the slot
The team at whendca.com runs a public DCA timing calculator built on the same idea. Their current read: the 19th beats the 22nd by 1.83% on monthly buys, Saturday beats Monday by 1.01% on weekly buys, and 07:00 UTC beats 20:00 UTC by 0.43% on daily buys.
Put the two analyses side by side and the takeaway writes itself. Their best weekday is Saturday, ours is Thursday. Their best hour is 07:00 UTC, ours is 01:00 UTC. The “best” slot depends on the window you measure. DCA timing edges are real, small, and unstable. Anyone selling a perfect buying schedule is selling something.
Why mid-month days might win
No clean causal story emerged from the data, and readers should be skeptical of anyone who claims one. The usual suspects are weekend liquidity dips and month-end fund flows, plus early-month salary buying pressure. Note that our data actually shows early-month days performing worst, which cuts against the salary story. In noisy data, 1 to 2% edges rarely come with clean explanations. Treat the pattern as a tilt, not a law.
What matters more than timing
Three things beat the day you buy.
Fees first. A 1% spread or a flat withdrawal fee erases the whole timing edge. Use a venue with low recurring-buy fees and cheap withdrawals.
Automation second. DCA works because you never miss a buy. Set the schedule and leave it alone.
Custody third. Coins left on an exchange are an IOU. Withdraw to a wallet you control.
Where Lightning helps
Lightning makes the automation part cheaper to finish. Services with Lightning withdrawals move your sats to your own wallet instantly for fractions of a cent, so the coins do not sit on an exchange between buys. You keep the schedule and you keep custody. That combination is worth more than any lucky calendar day.
The bottom line
If you want the best setup this dataset supports: buy on the 18th, or on Thursdays, in the early UTC hours. Expect roughly 1 to 2% over the worst timing. Then stop optimizing the calendar and focus on fees, automation, and getting your coins off the exchange.
FAQ
Should I switch my DCA day to the 18th?
If it costs you nothing, sure. Do not pay fees or break your automation to chase 2%.
Does DCA beat buying a lump sum?
Different question. Lump sums win on average in rising markets. DCA wins on behavior: it keeps you buying through drawdowns, which is when the strategy does its best work.
How often should I buy?
Weekly smooths your entry slightly more than monthly. Daily adds little once per-transaction costs are counted. Pick the schedule you will actually sustain for years.
