The situation
You open the conversion step and see two main choices: a fixed amount or a % of available balance. Both sound simple. But one common misunderstanding can turn a "small weekly top-up" into a much bigger sale than you intended. Here is how each one behaves, using only BTC quantities so the math stays clear.
The key fact
For percentage rules, the app's Review text states that Coinomatic "recalculates the percentage from the current available balance at each execution."
That means the percentage applies to everything available in that asset on your exchange account at run time. It does not apply only to what arrived since the last run. Coinomatic doesn't know which BTC you think of as "this week's payout" and which as "my savings." If both sit in the same account, a percentage rule sees them together.
Illustrative example – the 50% surprise
Illustrative example – made-up balances, BTC only, not a recommendation.
A miner holds 0.50 BTC of long-term savings on Kraken. This week, pool payouts add 0.05 BTC. Available balance at run time: 0.55 BTC.
- Rule: Fixed amount 0.02 BTC; What gets converted this run: 0.02 BTC
- Rule: 50% of available balance; What gets converted this run: 0.275 BTC (half of 0.55, not half of 0.05)
- Rule: 50% of available balance + Minimum balance to keep 0.50 BTC; What gets converted this run: 0.025 BTC (50% of the 0.05 BTC above the 0.50 reserve)
Without the reserve setting, the "50% of my payout" plan converts more than five times what the miner had in mind.
The interaction between the percentage and the minimum balance is exactly the kind of thing to check with a small test before you rely on it.
How the two rules compare
- Aspect: Entered as; Fixed amount: BTC (no USD/EUR target available); % of available balance: Percentage
- Aspect: Same each run?; Fixed amount: Same BTC quantity; % of available balance: Changes with your balance
- Aspect: USD result; Fixed amount: Varies with BTC price; % of available balance: Varies with balance and price
- Aspect: If balance is too low; Fixed amount: Run is skipped and logged; % of available balance: Converts a smaller amount; may fall below exchange minimum
- Aspect: Protecting a reserve; Fixed amount: Implicit (only the fixed amount is used); % of available balance: Use Minimum balance to keep
- Aspect: Limiting a big run; Fixed amount: Not needed; % of available balance: Use Maximum cap per execution (BTC)
- Aspect: Our verification; Fixed amount: Live tested (one run); % of available balance: Fields visible; execution not verified
How Coinomatic helps you set it up
In Step 2 of 6 – Conversion:
- Asset to convert: BTC.
- Conversion rule: Fixed amount, or % of available balance.
- Percentage to convert (for the percentage rule).
- Maximum cap per execution (optional, BTC): an upper limit for any single run.
- Minimum balance to keep (optional, BTC): a floor that isn't converted.
While you type an amount, the step checks the exchange's minimum order size. If the amount is out of range, the field turns red. If it's fine, the "Checking the minimum order size…" message disappears.
Review then restates the rule in words (e.g., "50% of current available BTC balance") before you confirm.
Time check
Model example, your numbers will differ.
The rule type doesn't change much in our time model. Frequency does. For a weekly routine (≈4.3 runs/month) with a manual run ≈17 min, an automated check ≈2 min, a monthly review ≈10 min and setup 20 min / 12 months:
4.3 × (17 − 2) − 10 − 1.7 ≈ 53 minutes a month, modeled.
One honest addition: a percentage rule produces a different amount every week, so you may want a slightly longer check per run (say 3 minutes instead of 2). That would reduce the modeled savings to ≈49 minutes. The "check" minutes are where you'd catch a 50% surprise.
Limits and how to check the result
- No dollar-denominated fixed amount at the time of our test.
- Percentages of a shrinking balance get smaller and can eventually hit the exchange minimum (ORDER_SIZE_TOO_SMALL).
- Fees are set by the exchange and apply to each run.
- No guaranteed amounts. Coinomatic "does not optimize execution or make financial decisions."
- How to check: before saving, write down your current available balance and work out the first run by hand. After the first run, compare it with the BTC amount in Transactions.
Next step
If you hold savings on the same account, read article 13 on treasury buffers. Then set up the rule using the Knowledge Base guide Create an automation, starting with a one-run test.
Coinomatic is software that triggers actions on your connected exchange account (today: Kraken) based on rules you set. It is not a financial advisor, broker, or money transmitter, and it does not take custody of your funds. Nothing in this article is financial, tax, or legal advice.