Calculator inputs
Enter time points and matching survival probabilities as comma-separated lists. The tool assumes a stepwise survival curve and integrates area up to tau.
Example data table
| Time | Treatment survival | Control survival | Interpretation |
|---|---|---|---|
| 0 | 1.00 | 1.00 | Both groups start event-free. |
| 3 | 0.94 | 0.90 | Treatment retains more event-free probability. |
| 6 | 0.88 | 0.80 | The gap widens by month six. |
| 9 | 0.79 | 0.69 | Area between curves contributes to RMST difference. |
| 12 | 0.70 | 0.57 | Restricted average survival still favors treatment. |
| 18 | 0.58 | 0.46 | Use these values as a quick sample dataset. |
Formula used
Restricted mean survival time measures average event-free time from 0 to a chosen horizon tau.
RMST(tau) = integral from 0 to tau of S(t) dt
For stepwise survival values, the calculator uses interval rectangles:
RMST(tau) ≈ Σ S(t_i) × (t_(i+1) - t_i)
When tau falls inside an interval, the last width is truncated at tau. The tool also reports:
- LMST(tau) = tau - RMST(tau)
- RMST difference = RMST_A - RMST_B
- RMST ratio = RMST_A / RMST_B
- Event-free person-time = RMST × cohort size
How to use this calculator
- Set the restriction time tau in your preferred unit.
- Enter one survival curve using matched time and survival lists.
- Add a comparator curve when you want an RMST difference.
- Keep times strictly increasing and survival values non-increasing.
- Submit the form to view summary metrics, interval areas, and the chart.
- Download CSV for spreadsheets or PDF for reports.
Frequently asked questions
1) What does RMST mean?
RMST is the average event-free survival time accumulated before a chosen cutoff. It summarizes the whole curve up to tau, not just one time point.
2) Why use RMST instead of median survival alone?
Median survival only reflects where the curve crosses 0.5. RMST uses the full survival pattern up to tau, so it can remain informative even when the median is not reached.
3) What should I enter for survival probabilities?
Enter stepwise survival levels between 0 and 1. Each value must match a time point, and the sequence should stay flat or decrease as time increases.
4) What happens when tau is beyond my last time point?
The calculator extends the last observed survival level horizontally until tau. That keeps the step-function assumption consistent for restricted area estimation.
5) Can I compare two study arms?
Yes. Add the comparator curve to estimate RMST for both arms, the RMST difference, RMST ratio, and survival difference at the same horizon.
6) What is lost mean survival time?
Lost mean survival time equals tau minus RMST. It represents the average time not spent event-free before the restriction horizon.
7) Does this calculate confidence intervals?
No. This page focuses on deterministic area estimation from supplied survival values. Confidence intervals need variance inputs or raw patient-level survival data.
8) Is the chart based on interpolation?
The graph uses a horizontal step curve, which is the standard interpretation for Kaplan-Meier style survival values between entered event times.