Does the Polar API have an MRR endpoint?

Yes. GET /v1/metrics/ with metrics=monthly_recurring_revenue returns Polar's own MRR per interval. That is unusual among payment providers, most of which make you derive MRR from a subscriptions list.

How does Polar define MRR?

Active subscriptions normalised to a month, with yearly plans divided by twelve and trials excluded. It is the same definition the Polar dashboard shows, so an API figure and a dashboard figure agree.

Why does the Polar metrics endpoint return null for today?

Polar computes metrics on a pipeline and the newest period can be null until it catches up. Read the last period that has a value rather than the last period, or your figure reads zero shortly after midnight.

Which timezone does the Polar metrics endpoint use?

Whatever you pass in the timezone parameter, and Polar's default if you pass nothing. Pass an IANA name such as Europe/London rather than an offset so daylight saving is handled.

What is the Polar sandbox API URL?

sandbox-api.polar.sh, against production's api.polar.sh. A token from one used against the other returns 401, which looks like a bad token rather than a wrong host.

How to calculate MRR from the Polar API

Does Polar have an MRR endpoint?

Yes, and that is unusual. Most payment providers make you derive MRR from a subscriptions list and argue with yourself about the definition. Polar computes it server-side and serves it from /v1/metrics/.

curl -s 'https://api.polar.sh/v1/metrics/?start_date=2026-09-01&end_date=2026-10-01&interval=day&metrics=monthly_recurring_revenue' \
  -H 'Authorization: Bearer polar_oat_...'

The response carries a periods array, one entry per interval, each holding the metric values you asked for.

What Polar's MRR counts

Active subscriptions, normalised to a month. Yearly plans are divided by twelve. Trials are excluded. That is a reasonable definition and, more usefully, it is the same definition the Polar dashboard shows, so your number and the one your co-founder is looking at will match.

Ask for metrics=monthly_recurring_revenue explicitly. The endpoint will compute fifty-odd figures per call if you let it, and asking for one is faster and kinder.

The trap: null periods

Polar computes metrics on a pipeline, and the newest period can come back with null for a while before it is filled in. Code that reads periods.at(-1) will show zero shortly after midnight and then correct itself.

function latestMrr(periods) {
  // The last period with a value, not the last period. A null newest
  // bucket is a pipeline that has not caught up, not an MRR of zero.
  return (
    [...periods].reverse().find((p) => typeof p.monthly_recurring_revenue === "number")
      ?.monthly_recurring_revenue ?? null
  );
}

Ask for a week of daily periods rather than one, so there is something to fall back to.

Timezone

/v1/metrics/ takes a timezone parameter and it is worth passing explicitly. Omit it and your daily buckets follow Polar's default rather than yours, and every figure near midnight lands on the day you did not expect.

Use an IANA name, Europe/London rather than an offset, so daylight saving is handled for you.

Sandbox and production are different hosts

Polar's sandbox lives at sandbox-api.polar.sh and production at api.polar.sh. A production token against the sandbox host, or the reverse, returns 401. That is better than returning an empty account, which is what several providers do, but it still looks like a bad token rather than a wrong host.

When to compute your own instead

Polar's figure is the right default. Compute your own if you need a definition Polar does not offer: MRR excluding a particular product, MRR by plan tier, or a figure that nets off a discount Polar counts differently.

In that case list subscriptions and normalise each one yourself, the same way you would on any provider. Be aware that you are now maintaining a number that will drift from the dashboard, and that somebody will eventually ask which is right.

Or put Polar's own figure in the notch

Notch Metrics reads Polar MRR from that endpoint, handles the null periods, and shows it in the MacBook notch. It also reports revenue, active, new and churned subscriptions, and a feed of recent orders.

Connect once on the web, and the token never reaches your Mac. Download Notch Metrics.