Estimate runway on prepaid API credits

The code

This is the calculation Argus runs, minus the database:

type Sample = { at: Date; balance: number };
const DAY = 86_400_000;

/** Burn per day from a balance series. Only drops count, so top-ups don't cancel spend. */
function burnPerDay(samples: Sample[]): number {
  const s = [...samples].sort((a, b) => +a.at - +b.at);
  if (s.length < 2) return 0;
  let spent = 0;
  for (let i = 1; i < s.length; i++) {
    const drop = s[i - 1].balance - s[i].balance;
    if (drop > 0) spent += drop;
  }
  const days = (+s[s.length - 1].at - +s[0].at) / DAY;
  return days > 0 ? spent / days : 0;
}

/** null means no runway concern: no burn, or no known balance. */
function daysToZero(balance: number | null, burn: number): number | null {
  if (balance == null || burn <= 0) return null;
  return balance <= 0 ? 0 : balance / burn;
}

Where burn rates go wrong

• Top-ups. Diff the first and last reading and a $100 top-up looks like $100 of negative spend. Count only decreases.
• Too short a window. A one-hour eval run extrapolated to a day says you have hours left. Seven days smooths it; alert thresholds absorb the rest.
• Spend that settles late. OpenRouter's balance can dip slightly below zero after async settlement, and Bright Data deducts usage daily, so its balance moves in steps.
• Credits that aren't dollars. Firecrawl, Hunter and Apollo burn credits. Days to zero works in any unit; dollar totals need a price per credit.

Which number applies to which provider

For allowances, zero isn't the end: the allowance resets. Compare days to zero with days to reset. If the allowance lasts past the reset you're fine; if not, you'll hit the provider's overage or hard stop first.

Alert on it

Seven days of runway is a reminder; three is urgent. Argus raises credits_low at seven days and credits_critical at three, and you can set a days-to-zero email alert at any threshold. See low-balance alerts for what each console offers natively.

Questions

How do I calculate how many days of API credits I have left?

Divide the current balance by your average daily burn. Measure burn from balance drops over the last 7 days, counting only decreases so top-ups don't hide spend.

Can I estimate runway for OpenAI or Anthropic credits?

Not from their APIs alone: neither exposes the prepaid balance. You have the daily spend series, so you can project month-end spend against your monthly cap, or record the balance yourself after each top-up.

Related

OpenRouter API usageDeepSeek API usageFirecrawl API usage