The mechanics
No magic. A reserve, a rate, and a date.
Larkspur is four rules applied to money you already earned. This page is the whole thing — the arithmetic, the timing, the edge cases, and the situations where we would tell you not to bother.
Step by step
Four rules, run every day.
Once you have set the rate and the buffer, Larkspur does not ask you anything again unless something is about to go wrong.
Ines, month four
Worked exampleThe remaining $4,685 stays in the reserve. Next month it is what pays her.
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Rule 01 · daily
Read what settled
Larkspur checks your business account once a day for cleared deposits. Pending transactions are ignored — a card payment that has not settled is not income yet, and reversing a set-aside is worse than waiting a day.
Checked at06:00 local, every day -
Rule 02 · on arrival
Move the tax off the top
Your rate is applied to the gross deposit and moved to a separate account in your name the same day. Gross, not net — because that is what the tax authority assesses. If you change the rate, the change applies from the next deposit forward; nothing is retroactively reshuffled.
Typical rate25–35% US · 30–40% UK -
Rule 03 · monthly
Size the paycheck from a trailing average
Larkspur takes a twelve-month trailing average of post-tax income, subtracts the buffer rate, and rounds down to the nearest $50. Under twelve months of history it uses what it has and marks the figure provisional. The number is recalculated on the 20th and only ever moves once a month, so you always know it fourteen days ahead.
Recalculated20th · effective the 1st -
Rule 04 · the 1st
Pay it, or warn you
At 07:00 on the 1st the paycheck moves to your personal account. If the reserve cannot cover the full figure, Larkspur emails you on the 18th of the previous month with the reduced amount and the reason. It will never overdraw the reserve to hit a number.
Notice before a cut14 days, minimum
The actual math
Written out, so you can check it.
There is no model and no prediction. Larkspur is an average, a percentage and a subtraction. Here it is on a real year — $84,600 of revenue arriving in six uneven lumps.
Sizing the paycheck
Rounding down is deliberate. The rounding remainder stays in the reserve, which is why the reserve grows very slightly faster than the buffer rate alone would suggest.
Sizing the reserve
Above six months of cover, Larkspur stops adding to the reserve and tells you to move the excess somewhere it earns something. It is your money sitting idle, and we would rather say so than quietly hold more of it.
Every figure on this page is illustrative. Your rate, your buffer and your history produce different numbers — the calculator on the overview page runs the same arithmetic on figures you type in.
Runway, live
How long does the reserve actually last?
The question behind the question. Move the sliders — Larkspur runs this same calculation nightly and shows the result on your dashboard.
Your position
What-ifOutgoings means everything leaving the business and the household — rent, tools, contractors, your own paycheck.
Months of cover
4.1months
Reserve empty around July 2026
Tax timing
The dates, and what Larkspur does on them.
| Date | What it is | What Larkspur does |
|---|---|---|
| 15 January | US Q4 estimate for the prior year | Emails the figure on 2 January with the tax account balance beside it. |
| 31 January | UK balancing payment + first payment on account | Emails on 4 January, and flags if the set-aside looks short. |
| 15 April | US Q1 estimate | Emails on 1 April. Nothing is paid automatically — you or your accountant file. |
| 15 June | US Q2 estimate | Emails on 1 June, plus a mid-year rate check if income has moved 25%+. |
| 31 July | UK second payment on account | Emails on 4 July. |
| 15 September | US Q3 estimate | Emails on 1 September. |
Larkspur does not file and does not pay the authority on your behalf. It holds the money in an account you own and tells you when to move it. That is a deliberate limit, not a missing feature.
Honestly
When this doesn't work.
Under six months of trading
There isn't enough history to average, and no reserve to smooth from. Larkspur will let you start, but the first paycheck is small and the figure moves every month until you have a year behind you. Most people are happier waiting.
Income that is genuinely falling
Smoothing a decline just moves the problem three months out. Larkspur detects a sustained downward trend and drops the paycheck rather than draining the reserve — which is correct, and also not what anyone wants to hear.
One client, one invoice a year
A single annual payment isn't lumpy income, it's a lump sum. A savings account and a calendar reminder will do the same job for free, and we will tell you that on the setup call.
You need the money now
The reserve takes two to three months to fill from your own income. If cash is tight this week, Larkspur makes it tighter before it makes it better. Start when you have a quiet month, not a desperate one.
Find out what your steady number is.
Connect an account read-only, or just type six months of figures in by hand. Larkspur tells you the paycheck it could hold, before you commit to anything.
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